Patrick... that's what I had understood you to be saying, that the complete assembly was about the same weight, but the particular components varied, in different versions.
I take it that your comment about 2-stroke cranks for 4-strokes is a reference to the crankcase / flywheel clearance and hence the skimmed wheels. Lots of old 4-strokes are like that. I don't know about H-D, but a number of early 30s British designs such as the Blue Star BSA, Panther singles and some Royal Enfields relied on crankshaft oil fling to get the oli around the scavenge pump, or back into a front-mounted wet sump, hence the very tight clearances, and the feature was just carried forwards for many years afterwards because no-one thought to change it.
That's one reason you sometimes see early Gold Stars with case failure - the oil locks between the flywheel and the case. Later ones are slightly different, just as you describe. There are other reasons that Goldies break their cases, though!!
I know what you mean about there being no standard KRs anywhere, ha ha. I don't know KRs but I have a fair amount of experience of racing JAP singles, and they are about the same.
There are umpteen variants; a 350cc, four main versions of the 500cc such as long and short con-rods and different numbers of head bolts; long-stroke and short-stroke 500cc versions - note that the stroke and con-rod variants are not the same. The differing con-rod lengths are to change the power characteristics by varying the crank geometry and rod angles during the powerstroke.
Most of the main sub-assemblies more-or-less fit together to give several other possible combinations, most of which require irreversible alteration to main components ( eg ultra-short-stroke 500cc using 350cc crank, oversize 500cc using long-stroke crank and short-stroke barrel, 350cc engines with oversize ports using 500cc inlet valves, welded cases to give later 4-stud top ends on earlier 5-stud cases, about the only one you DON'T see is a possible oversize 350cc using 500cc parts; this is because the scrutineer would spot it straight away and either disqualify it, or put it in the next class up against full 500cc engines - no good! Plus quite a lot of the ones now running use late-model 84S parts for reasons of availability )
I do have a 'three-two-five' BSA engine in my workshop, ie a 250cc BSA C15 using a 71mm Triumph piston; this gives abou 325cc, hence the name, and is visually the same as the original.. but we won't go ino that.... they were quite common at one time!
Shoot, a man could have a good weekend in Dallas with all that stuff...