hey Froze, AGK sells a chain-drive transmission that will work. Check it out
. You'll need a motor mount plate, rear sprocket, throttle, and fuel tank too. You could re-use the HF fuel tank if you can find an appropriate place to put it tho.
With your weight, a Huasheng would work, too. My motorized bicycle and I together weigh about 300lbs, but my little Huasheng doesn't have problems getting me up most hills. Huasheng is a little more expensive than a Pred and has less power, but it's a legal engine.