(I am going to assume that Chiang controls the entirety of the country. Also, some of my ideas may be a bit impossible
).
A KMT- led China will be an entirely different beast than Taiwan. As mentioned by others before, the latter was a small, relatively tightly populated area that had been inflicted relatively less damage than other places, relatively developed infrastructure and a rather well-educated (or at least literate) population. The former, on the other hand, was a vast and impoverished country, with very little infrastructure and industry left intact : the progress that had been made during the Nanking Decade had been destroyed by the war, while in Manchuria the Soviets had picked up the best parts. Also, in Taiwan, the economic miracle largely began after Chiang's death, under his son's auspices and was part of a more extensive liberalisation campaign that was (to a large extent) the result of pressure from the domestic opposition. With all these in mind, I think that a KMT-led China is in a somewhat disadvantageous position compared to a KMT-led Taiwan; but still, if Chiang can deal with issues like widespread corruption, the country's disunity due to the existence of the many warlords and their private armies and bring stability, I think that the Chinese economy could flourish. I am going to work on these assumptions in this case. I will cover the 1950s-1970s period, since I think that it would be the decisive period.
1945-1949: the Chinese civil war. In order to win a measure of support from the peasantry, Chiang could promise land reform (although a not very specific one). With some convincing propaganda backing it, it could sway a potentially large number of peasants to support the KMT. The Americans also support the Chinese government to curb the hyperinflation somewhat. These two, combined with some Communist blunders enable the Nationalists to win in 1949. Let's assume that Stalin doesn't decide to intervene in the final stages of the war by sending troops in Manchuria or Sinkiang (perhaps due to a longer and more intense crisis in Berlin and more strained relations with Yugoslavia). This gives Chiang the entire country.
1950s: I find it very difficult for the Korean War to happen ITTL as well, since now, North Korea is sandwiched between China and South Korea. Furthermore, the recent failure of the Communists in China would have possibly discouraged the North Koreans to invade. Thus there are two possibilities :
If the Americans limited their participation in the Chinese civil war to material and financial aid and Stalin was neutral for most of it, then Sino-Soviet relations are better in 1949 and Stalin may think that the United States are unwilling to intervene in Asia. Also, by 1950, the Soviets would have detonated their first nuclear bomb, breaking the nuclear monopoly of the USA and the Americans would have even less reasons not to pull out of Korea, now that the Communists have been defeated in China. Thus, if Stalin could get China to remain neutral in a potential conflict (in exchange for his neutrality during their civil war and his non-intervention in Manchuria and Sinkiang), he could feel more secure with pursuing a more aggressive foreign policy in Asia and allow Kim il-Sung to attack South Korea.
The Americans would react to this development, but possibly not directly; instead, they would try to get Chiang to intervene. Chiang would initially refuse, as he wouldn't like to antagonise the Soviets; but a combination of US threats to cut off aid or reduce it considerably and severe ties with his regime, the threat of a communist Korean state which would increase the danger for the industrial heartland in Manchuria and finally, a potential desire to expand Chinese influence in Korea, which was after all for much of its history in the Chinese sphere could make him change his mind and decide to intervene against the Communists. Stalin wouldn't be happy at all, but he also wouldn't want to bleed the Soviet army in a war with China. Therefore, the Chinese invade from the north, while the Americans forces make some landings in the south. The Korean war ends in late 1951 with the entirety of the peninsula being under US and Chinese control.
This change of heart on Chiang's part would make Sino-Soviet relations worse for quite some time. The Sino-Soviet border in Manchuria would be more militarised and the Soviets would likely hang on their economic assets in Manchuria such as Port Arthur and the Manchurian Railroads for a longer period of time. At the same time, Chiang would tie China more closely to the United States. This would result in several things:
Military: The Americans would fund a drastic expansion and modernisation of the Chinese army and would be the main supplier of arms; the goal would be to create a Chinese military with the ability to hold its ground against a Soviet attack and if possible, counterattack. The proximity of the Soviet threat in Manchuria could lead to a large military build-up in the area, which would spur the growth of related sectors there (construction, services, military-related industries). The Daqing oil fields would be also developed and refineries would be built nearby in order to create a source of fuel for military purposes near the front, thus making supply lines shorter (although this would also make the former more vulnerable to Soviet attacks). There is also the possibility of the Republic of China beginning to build a navy of its own, which would lead to the foundation of a significant shipbuilding industry. All these would create a lucrative arms market for the American and European arms industries. The British government in particular, chronically short of cash, could be very interested in selling wartime equipment to China and make some money out of it. Chiang, in an effort to ensure continued Western support, would encourage these developments. Also, with China being the main recipient of military aid and the main frontline state of the Cold War in Asia, Korea and Japan would receive less in that sector.
As far as the Soviets are concerned, they would have to face an even longer unfriendly border. This in turn would force them, at least in the short term, to rump up military spending. This could lead to an earlier realisation in the future that the Soviet economy is in trouble (see more below). The prospect of a major potential front in the Far East would result in an increased military presence in the area. Perhaps Stalin decides to make the Transiberian Railroad double-tracked in order to improve communications between Moscow and the front there. There would be a larger decree of industrial development in the area, as well as development of economy sectors related to the military. Vladivostok in particular would benefit from these developments, but not as much as people would expect, as the Soviet government would invest heavily in Port Arthur as a base for Soviet submarines to interdict enemy shipping in the area.
Main Economy: There would be an influx of American capital in China, either as aid or investment. As a result of the war and the previous era of instability, China would be something close to an economic "virgin land". The watchword would be (Re)building, as almost the entire country had either been devastated by the war or left undeveloped. This would result in a very large demand for things such as industrial machinery, fertilisers, modern agricultural tools, tractors, construction equipment, mining equipment etc, which would be necessary for the agricultural and industrial development of the country. There would also be a very large demand for goods such as medicine and medical equipment, typewriters, necessary to organise some basic services for the population and the administration of the country; consumer goods, on the other hand, wouldn't have such a large market, since much of the population would be rather impoverished and the main buyer would be the government; but if there is a general economic upturn, a growing consumer goods could possibly have developed by the late 1950s. There would also be large-scale infrastructure programmes. At the same time, (hundreds of) thousands of American specialists (doctors, engineers, agronomists etc) would go to China to offer their services
All these would create a very lucrative market in China and many western countries would rush to take a part of it. The United States would most likely hold the lion's share of it, thanks to its larger economic power but also due to the influence it has over the Chinese government. This increased demand for American products would lead to a need for increased production; given that unemployment was already low at the time, this would push wages upwards and thus increase blue-collar and middle class prosperity, which in turn would spur even more domestic growth. There is however the possibility that if this increased buying power isn't matched by a corresponding increase in the amount of available consumer goods, the combination of higher wages for many people and already significant government spending could begin to slowly build up inflationary pressures in the economy.
European countries could also gain access to the Chinese market. Although Britain and France may be somewhat unable or unwilling to interact with the Chinese regime (the former due to the issue of Hong Kong, which could arise ITTL and also due to the problems they will probably face in Malaysia, the latter due to potential friction over French Indochina), others, like Germany or the Netherlands would try to enter this new market. In the case of Germany, closer economic relations with China could spur even greater economic growth and might have laid the foundations for a resumption of a sort of Sino-German cooperation later on, as there is already a precedent to this and Chiang may think that the Germans, due to their distance and their postwar position could be safer partners. Also, the non-participation in the Korean War could mean that Britain continues its demobilisation and transition from a war economy to a peace one would be uninterrupted. Thus, money which IOTL was diverted to fund the military operations in the Far East could be funnelled into the further reorganisation and reconstruction of industry, while this last process would be completed and not interrupted by the war. There is also the possibility that, with the less menacing perception of the Soviet Union's presence in Europe and the better economic transition after the war, Britain would be able to maintain its empire for longer; if it managed to improve the colonial economies and make them reliable partners, then the benefits for the British economy would be significant. France could also have at forcing a negotiated settlement in Indochina, as the Vietminh would lack the support that China offered them between 1949 and 1954, while the Vietnamese would be fearful about potential Chinese designs in the area, especially if Chiang tried to help the VNQDD; thus, France could actually win the war on the field and force through a negotiated settlement that enabled them to retain their influence in the area; this success in turn could help the French reform their empire in Africa better. If all these happened, there is also a possibility that the EEC wouldn't be developed, at least for the time being, as Britain and more importantly, France are more interested in maintaining and integrating their empires and their cooperation hasn't been tainted by events like Suez. Again, in the case of Britain, this could lead to the development of state-of-the-art and competitive industries in defence and electronics, sectors where Britain had many advantages and which could be very useful, while the survival of a Sterling Bloc (partly thanks to a relatively stronger British economy) and a Commonwealth trade zone would also be positive additions.
As far as Japan and Korea are concerned, the victory of the Kuonmintang in China would divert most of the aid they received in OTL as military assistance; in the case of Japan, in particular, the fact that this state wouldn't be at the frontlines of the Cold War ITTL, as the main focus would be in China, would lead to a more thorough demilitarisation, with only a somewhat more heavily armoured National Police Reserve being allowed. This means that there would be even less military expenditures, while the Chinese civil war and the Korean conflict would enable an economic recovery. There would also be a more thorough reorganisation of the Japanese economy, as there wouldn't be as much pressure as IOTL to prioritise the quick recovery of the latter. Thus, land reform would go through, as OTL; also, there would be more robust anti-trust legislation and at least for now, the Keiretsu wouldn't be allowed (at least officially) and in general, economic recovery would be rather slower than OTL. However, the existence of China as a large market with great demands could compensate for these disadvantages, as there would be adequate demand to stimulate production in Japan in order to sell these products in China; if the Americans developed a coordinated plan to use the vast market in China to facilitate Korean and Japanese recovery and reconstruction through trade between these countries and supported it by offering funds, the resulting sustained increase in exports would benefit Japan. Combined with a probably quieter domestic front, as there are less controversial issues, such as rearmament, and the LDP and its first Prime Minister, Nobusuke Kishi don't rise to power (the former probably wouldn't be created as there is less need to create a bulwark against the Socialists, who would be weaker and certainly not Maoist), there is a possibility that Japan's economy would grow at a rather slower but still impressive pace.
Regarding Korea, the less extensive damage sustained during this alternate Korean War and the fact that the united country has more resources and people means that prospects for economic growth are somewhat brighter. Furthermore, the lack of an immediate threat means that the United States would probably be less willing to accept Rhee's antics and corruption and would either force him to change course or remove him. This, combined with a more relaxed domestic situation could enable Korea to experience an earlier economic miracle.
As for the Soviets, the aforementioned increased military spending could lead to a somewhat slower reconstruction that could hamper economic growth to a certain extent. This in turn could make the subsidisation of the USSR's satellites in Eastern Europe a bit more expensive, which in turn might create more support for the implementation of Yugoslavia-style economic reforms (and in general, an overhaul, extensive or limited, of the economy).
1960s: As the 1950s would come to an close, China's reconstruction phase would come to an end as well. The creation of a large and fairly modern industrial base in China and the desire of the Chinese government to sustain growth at high levels, combined with the development in communications, the lower labour costs and the more lax labour laws in China could lead to an early beginning of outsourcing, primarily from the United States, where the overall lower than OTL unemployment rate and the greater prosperity, would create a labour shortage for the crappier jobs in the industry. All these factors would lead to the beginning of China's rise as an export country, as well as plant the seeds of a potential US-Chinese conflict in the future. In the Soviet Union, a combination of certain economic reforms and a more realistic approach to the military needs of the country would probably allow the Soviet economy to stabilise. There could also be an earlier attempt at detente, at least with European countries, in order to decrease the burden of military maintenance somewhat. Relations with China could begin to thaw in the second half of the decade, as China tries to move to a more independent position diplomatically and balance the American influence. As far as Europe is concerned, increasing US opposition to the survival of the British and French colonial influence could lead the two countries to both move closer to each other and also seek to integrate Europe closer to them (particularly France). This, combined with the end of reconstruction that made close ties to the United States absolutely necessary and a growing opposition to American policies abroad (we could assume that success in China would make the United States more interventionist) could result in the formation of closer economic and trade ties between the various European countries. Many European countries could also benefit from a potential Chinese move to diversify its trade partnerships and decrease overall dependence on the USA by building closer trade and business relations with Europe.
The main impacts of a KMT China during this decade would be, in my view, two. The first one would be the spread of its system of state capitalism in East Asia and the Third World, as more countries would be interested in replicating China's success in developing a modern economy while being a country that lagged behind considerably compared to Europe and North America. Also, the need to compete with China could lead Japan and Korea to shift more quickly than OTL to new industries such as electronics and also, to enable the creation of larger business entities unofficially backed by the state and seek new markets.
The second one would be China's impact on the world's financial and monetary systems. IOTL, the global banking and financial system was built around the primacy of Western Europe and North America. This process was finalised in the 1960s. However ITTL, the presence of China and its greater participation in the international economy in the 1960s is going to change this. The survival of Shanghai as a trading and banking hub, as well as the large amounts of capital that had entered the country in the 1950s means that China has a larger impact in global finance and banking. This could lead to the rise of a "Sinodollar" market in the 1960s, as a Pacific analogue to the Eurodollar market, which would in turn lead Shanghai to rise as an international financial centre, at the expense of the City, which could however compensate for this by the survival of the Sterling Bloc mentioned above. This latter development could also lead to the creation of a smaller 'Sinopound" market in Hong Kong, especially if relations between Britain and China remain somewhat cordial and stable.
1970s: The time of change. China is now an extensively developed and industrialised country; outsourcing to the "sweatshop of the world" has become more prevalent while Chinese exports continue to rise in fame. All this newfound economic power could give rise to ideas for a more independent position of China in the Cold War. At the same time, the Western economies undergo extensive transformations.
In the United States, the more extensive outsourcing, combined with the rise of multiple competitors abroad in Japan, Korea, Europe and China are going to weaken the manufacturing sector more than OTL during this period. If an energy crisis like the embargo of 1974 happens ITTL too, the combination of a weaker manufacturing sector, rising inflation and anaemic growth would lead to a worse stagflation crisis than the one experienced IOTL. If a progressive administration dominates the period, then we could expect things like efforts to repatriate industrial capacity (to an extent), negotiations with China about trade and exports, cooperation with Europe and China to resolve the issues of high inflation, currency stability and trade imbalances, cooperation with the Soviet Union in an effort to bring down energy prices and efforts to create a new stable framework for the international monetary and financial system; if a more conservative administration rose to power, we could in turn expect a greater dedication to fighting the Cold War, which would subordinate to an extent the economy to political and strategic considerations and a form of neoliberal economics: thus, there would be largely token efforts to address the issues in trade, manufacturing and the international monetary and financial system, measures such as the unofficial "bonds for oil" agreement with Saudi Arabia to sustain the dollar's position in the markets and an earlier and more extensive deregulation and beginning of financialization than OTL.
The Soviet Union would actually benefit from a turn of events like this. With a much larger demand for oil than OTL, since there is also China to be considered and a Middle-Eastern embargo, there is an even larger and more lucrative market for Soviet oil, which could generate even more profits for the Soviet government. This, combined with the weaker position of the West could prompt the Soviet leadership to focus more on the domestic front. If the "oil diplomacy" managed to further improve relations with Europe, where the economic downturn and an earlier turn of America to the right could lead to more social democratic and socialist governments coming to power, and China, whose leadership would begin to try to charter an independent foreign policy (and rapprochement with the Soviet Union could offer both economic -namely affordable oil supplies and trade agreements- and diplomatic - namely a balancing of the two superpowers), then these revenues, together with some further reductions in military spending which would free up resources, could lead to an increase in the production of consumer goods and some further reforms in the economy.
In Japan and Korea, a potential energy crisis would cause troubles, but not as extensive as IOTL, as the two countries had transitioned earlier on to more modern technologies. The growing rift between China and the USA could also benefit them significantly, as more investments and aid could be directed towards them, while they would be under the radar, since they haven't managed to achieve the levels of exports in the USA that IOTL began to alert some in the late 1970s. Also, increased competition with China would prompt them to focus more an combination of very high quality and affordability for their products, as well as reforms in their corporate culture (more freedom for engineers, promotion by merit and not only by seniority etc) in order to enhance productivity and spur further innovation.
In Europe, the general economic downturn could lead the countries there to get closer to each other and develop a more robust common market in order to minimise the upheaval caused by the high energy prices and the economic destabilisation worldwide and also, as a means to protect domestic economies more effectively. This however wouldn't be easy, as Britain and France would be rather hesitant to open up their special economic and trade zones in their former colonies to the other European countries and there would be different views on matters like subsidies and regulations, as well as about whether the economic policy should take a turn to the left or the right, with the socialists and social democrats supporting measures like greater state intervention in and democratisation of the economy, higher taxes, more protective trade policies and more expansive welfare and, in the case of Britain and France, trying to carry out economic modernisation in the Commonwealth and French Union/Community nations in order to build them up, while the various conservative and liberal parties would largely support more reforms in the vein of the ones implemented in the United States by a conservative administration. There would also be a greater impetus to develop economic relations with the USSR as Chinese and American markets shrink (due to domestic industries taking the lead there and a a growing reaction to real or perceived unfair competition abroad respectively) and there would greater need for Soviet oil.
