i'd say port your stock jugs, get 30mm carbs, get a coolhead, and have your stock crank tured and welded.
call Jeff at F.A.S.T. racing, his website is www,farmandsandtoys.com
he will hook you a port job thats gonna give you power where you want it to be. that cheetah cub is gonna make no bottom end, very little if any midrange than its gonna hit hard as fuck when it hits about 8,000 rpms, then your gonna need to shift when it hits 10,500 rpms....not a fun trail motor imo...that narrow powerband is going to very difficult to keep on the pipe.
not to mention you will need a lockup clutch and an override tranyy if you go with the cub..