In fairness the Norrheimers probably had a winnowing period of the period Nazi crazies who came along or who adopted things too enthusiastically (I know I mentioned somewhere in here about some of them trying to be 100% period accurate in one characters internal monologue recollections). The material culture of the community will have a huge impact, too (small towns/cities are unlikely to generate horse archers, while ranching/herding communities are not going to field pike blocks).
They do tend to stick to the Viking motif pretty literally though. Kind of makes me chuckle on the inside picturing them running into the PEI survivors and pioneers and trying to take land from them by force in 50 or so years and they still haven't evolved beyond the shield wall tactics
Speaking
strictly about the military aspect:
The immediate post-Change (i.e. April 1998 - 2000 or so) security/defense/militia* of any sizable community (really small communities are likely to be just "adults with hunting weapons") is indeed likely to be some horrifically un-optimized pastiche of some historical model, with great dependency on the educational/recreational/intellectual backgrounds of the Founding leaders (or their immediate subordinates**).
So, yeah, expect to see slavish (and often completely upside down, due to lack of understanding or Hollywood influence) clones of <Viking Shield Wall, Roman Principate Century, Norman Foot Knights, Greek Hoplite Phalanx, etc>....but with ahistorical equipment (due to lack of fabrication capability or expertise...or better materials somehow being available), and very clumsy execution.
So the notional "Roman Legion Century" might be equipped with spears (the planners not being aware of the pila and its specifics), some form of sword (short or long), brigandine armor (possibly the easiest and quickest form of armor to fabricate on any scale), and some weird pattern of helmet that they could slap together on the fly. Its "tactics" being limited to marching straight up to an enemy and jabbing until they win.
Now, this is likely to undergo a serious re-boot (in those communities which survive and prosper), a couple of years after the Change, once the logistical situation (read: not starving, having a surplus of food, and the division of labor required to devote time to military issues) has changed. At that point, they've (the people who were office managers, farmers, and pizza deliverymen, not just soldiers and sheriffs and mayors) actually got some experience in military affairs (even if it's just beating off raids and patrolling), and can sit down to apply their knowledge of their particular situation while staring at every Osprey book and military manual they've been able to lay their hands on.
That's when you see properly optimized (and appropriate to the community's situation) military structures. IOW, Roman cohorts (with the troops wearing half/three quarter plate armor like 1500's pikemen) supported by archers and cavalry, with pike units in reserve.....rather than just a slavish clone of a Roman legion with all the limitations of the original (which do not apply to post-Change forces).
*- even communities founded/dominated by intact pre-Change military commands are going to be defended primarily by militia for a long time, there not being a deep enough resource/labor pool to support a nonproductive military class.
**- Go back and re-read DtF, and note how
little Juniper and Havel actually contributed to their community's military orientation. Chuck Barstow and Sam Aylward more or less design the McKenzie military structure and practice, with no input from Juniper (other than a sensible "Sounds good!"). Of all people, Will Hutton is most responsible for the Bearkiller military scheme (Havel set up the social order, with the A-List and Strategic Hamlet stuff), with Pamela a close second.
BTW, think about how long it would take (man-hours per) to produce the combat gear (weapons, armor, shield, etc) for just one guy. Even the most basic/easily-fabricated gear. Now multiply that time by a dozen, a hundred, five hundred, a thousand? Even with economies of scale and assembly-line production....you're talking being able to equip a single guy every day or so (for small/mid-sized communities).