if your gonna go 4mill cub, I would get it ported... there is more to be had out of the as cast setup... not as much as a set of stockers, but there is more in them, the 4mill cubs use a 115 rod and they use a 68mm blaster piston, the cub cylinders are taller than stockers so you dont have to run a spacer plate or cut into the domes, you can run a stock head on a cab if you have it milled and rechambered for the big bore, or you can run big bore domes with an aftermarket head, I would pick a site sponsor on here and give him a call, talk it over with him as far as what you plan on doing with the bike etc... they should be able to get ya the right crank, rods, pistons, domes etc.... they should also be able to help ya out with bike setup... because any good racers knows that just because you have a 100hp motor, dont mean its gonna be fast without the correct chassis setup....
if you plan on drag only, alky is the only way to fly....