Been a while since I have been poking around so I am a little late to the party, but this looks like another great project!
Not sure what you decided, but I can offer my 1st hand experience and opinion on the bearings. Opposing Tapered (Timken) bearings on the Chain side (properly preloaded) and flat rollers on the cam side. With Flat rollers on the cam side, you don't have to worry about expansion, binding, shimming between cases, etc, which would be a
major concern.
I can't speak for other models, but early Harley's used Flat rollers Until evolution came about in '57 and then used Tapered on chain side from then on out with flat rollers on cam side. This was a
major improvement in every singe way (1st hand).
I would use either flat rollers on both side (if you want an earlier period correctness) and thrust shims to prevent walk, or Timken on chain side and flat rollers (or bushing) on other but def not tapered on both sides.
Are you going to do an oiling system? Oil hole through shafts and flys into crank pin? ..you mentioned more displacement and more RPM than the last, but not how much more, haha

Regards,
Shawn