I think I performed your 'CT90 mod package' on all my early bikes. A bare frame with dozens of empty bolt holes was, like, ideal.

My first motorized vehicle was a Rupp Roadster II rolling chassis with a West Bend 510 (?) 2-stroke lawnmower engine and belt-drive torque converter. The T.C. was set up for a low-rpm Briggs/Stratton or similar four-stroke motor and never worked well, but a lot of fun was had nonetheless. This bike taught me that no mechanisms were so incompatible that machine shop doohickeys couldn't force them to work together.
I remember drilling out frame/swingarm tubes for shock mounts, cutting a hole in a rotary-valve engine side cover for a small disc filter (to let more air - and dirt - into the carb), replacing silencers with straight pipes, putting knobbies on a Yamaha YL1 100cc twin street bike, painting a Suzuki TS125 baby blue, etc. etc. I'm sure there were other things too, most of which I'd probably rather forget. ;>)
Ray