Thanks guys, for the fork discussion - gives me some more to think about.
Meanwhile, I totally disassembled the engine and some remaining sub-assemblies from the 1990 parts-bike today. The oil and water had mixed, and several bearings were not good. The worst bearing was the one in the cylinder block for the gear that drives the alternator - totally toasted and the engine case was severely blackened around the overheated bearing. This bearing seems to be rather weak in comparison to the rest of the engine - and you'd never know it was bad unless you removed the entire clutch housing.
However, the cylinder walls looked good, as did the main bearings and connecting rod bearings - after 180,000 miles.
I'm putting my Shinko rear tire on now and was second-guessing my choice of Y-spoke vs. 3-spoke wheels. So I decided to weigh the two rear wheels. Interestingly, the Y-spoke is nearly a full pound lighter than the 3-spoke. I expected the older wheel to be heavier.
1990 Y-spoke rear wheel weighs 10 lbs, 14 oz.
1992 3-spoke rear wheel weighs 11 lbs., 11 oz.
FYI - both wheels had no tire, but did have a valve stem and about the same amount of wheel balancing weights. For anyone who cares about unsprung weight, the older rims offer almost a 1 pound advantage, since I also like the looks of the y-spokes, I'm going to stick with those.