You need the long rod stroker crank, 795 pistons, either spacer plate with stock head or stroker domes with a coolhead type everything else can stay the same. I just built one and had it ported agressive trail and it runs with the YFZ450 all day. I also have some suspension work done and it helps to keep the power to the ground. It is about a 7% increase in all around HP with more bottom end than a stock stroke. If you can wait till you got the cash and do it all for the best effect.