I've seen several attempts, it usually involves ruining a perfectly good frame. They can be found in your local classifieds, usually unfinished, usually with a price that matches an unmolested one.
The go-kart type torque converters are bulky, not real sure where you'd put one without having it in the way of your feet. The 50/70 style clone engines are the go-to for a reason, they work. I understand using what you've got on hand, but is it really worth the effort to put a square peg in a round hole?
Hoarder of the finest junk
'82 YT175
'83 YTM200
'85 KLT110
'86 Moto 4 225
'84 TRX200 trike conversion.
'87 Tecate 4
Lots of vintage and not so vintage two wheeled stuff.