My thoughts exactly. I have an NOS one, and figured out (theoretically, on paper) how to mount it as a jackshaft/transmission, worked out how to put a sprocket onto the crankshaft, and while mocking it all up, realized the cables would be too short so the gripshift wouldn't reach. I could make new cables, but I've built a lot of custom motorized bikes, and just knew if I put it all together, shifting it under power would destroy those cheap gears, and the grip shift would strip out eventually. Sooner, not later.
With your set-up, at least for the gear replacement, it looks more plausible.
Sadly, I've had my fill of blowing up cheap chinese motors, and haven't built any in a while.