I agree with Hcira1. Reagan was a better campaigner than was Ford and not have the Nixon pardon, which outweighs the extremist reputation.
The actual election between Reagan and Carter in 1980 makes for an interesting comparison. Reagan won with a 9.7% nationwide popular vote margin, with a recession, the embargo, the Iranian crisis, and Carter's unpopularity with the Democratic establishment all hurting Carter. Reagan also carried 45 states. However, Carter ran close to Reagan in the polls during the campaign, and Reagan's nationwide popular vote total was 50.7%, only 2.7% higher than Ford got in 1976.
I think that without Carter's problems as an incumbent, the hypothetical 1976 race plays out like the actual 1980 race, with the polls being close , but the difference is that there is no sudden Reagan surge at the end, with him winning the nationwide popular vote by between 2% and 3%. He also wins the debates as long as he avoids making a gaffe.
In the OTL 1976 campaign, Ford carried eight states with less than 2% of the vote: Oregon, Maine, Iowa, Oklahoma, Virginia, South Dakota, California, and Illinois. Does Reagan's reputation as being more conservative mean he loses any of these, despite improving on Ford's nationwide popular vote total by 2% to 3%? I think he could lose Oregon, Maine, and Iowa, totaling 18 EVs. The other five were not as close and/ or Reagan's conservative reputation would have hurt him left. He is almost certain to lose Oregon, the closest Ford state and not all that conservative.
Carter carried Ohio, Wisconsin, and Mississippi with less than 2% of the vote, totalling 43 EVs. Reagan will at least carry Ohio and Mississippi and pick up 32 of these EVs.
Reagan needs a 29 EV swing to win, assuming he picks up the vote of the California elector who IOTL voted for Reagan. The electoral vote will be close. Taking Ohio and Mississippi and losing none of the Ford states gets Reagan to 273 and is enough. Carter's margins were 0.3% in Ohio and 1.9% in Mississippi. If Carter wins Oregon, Reagan will have to win Wisconsin (OTL 1.7% Carter margin) as well. Wisconsin had one more EV (11) than Oregon and Maine combined (10), so as long as Reagan wins Ohio, Mississippi, and Wisconsin, he can afford to lose both Oregon and Maine and still win. He has more of a problem if Carter also manages to win Iowa (1% OTL Ford margin), since the four next closest Carter states had margins of between 2% and 4%.
I went through the Senate elections in 1976, and the one place where switching the Republican candidates might of made a difference was Ohio, where Howard Metzenbaum, the Democrat, defeated incumbent Republican Robert Taft Jr. by a 3% margin. IOTL, Carter carried the state and this was the closest margin of any Senate election. In most of the other ones the margins were too big, and the few with small margins would not have been affected by the switch. ITTL, Reagan running 2% to 3% ahead of Ford and carrying the state could well have made a difference. Of course, Reagan being the incumbent after 1977 starts affecting the Senate elections in subsequent cycles. I suspect that if Taft wins, the Democrats still win that seat in 1982.
The OTL House of Representatives elections saw the Democrats make a net gain of a single seat, with an apparent 1.6% popular vote swing to the Republicans. I did go through the close races, and the problem here is that even with a slightly stronger presidential candidate, any additional seats the Democrats would have lost due to close races were in districts they would have likely won back in the better environment of the 1978 midterms, and with the one exception, the Congressman switched parties to the GOP anyway. Maybe an additional dozen GOP seats at the most, not much of a dent in the Democratic margin, and there aren't even many butterflies since the Democrats just win most of them back two years later.