With 2 new CB100 top fork bolts in hand, had another go using the S90 forks.
Worked as expected, though didn't cinch everything down very tight. At first, installed it with the S90 front wheel but then decided to test the CB100 front wheel/hub/axle but still using the early S90 forks.
Realized that the CB100 has the single diameter front axle but the early S90 forks would use the double diameter version.
So... either need to use late S90 forks (which are probably closer to the correct 1971 version) or just use the S90 front axle but with the CB100 wheel.
Unboxed the new tank and gave it a gentle clean. Added the cheap eBay cafe seat and also the soft center stand spring.
And we have a rolling chassis! Very cool to have her standing up on her own. Kinda looks great with all the empty space in the frame. Will need to preserve that as much as possible.