I plan to put a hsk600 on an eclectic scoter and I believe it has a 3/4in shaft. But the scoter has a #25 chain and I can’t find any #25 clutch or a #35 sprocket small enough.
I don't think you will be able to fin a clutch that size but i am also building a gas scooter from an electric and I am using a roller that rubs on the wheel directly, powered by a chain running from the engine. I don't know if it will work but I will try.