Because the early and late motors used different pistons. While both kits will physically "fit", the wrong combination could result in power loss, not gain. They assume a stock bottom end when spec-ing their kit.
See, there you go. Now why can’t Summit say that! Much appreciated Professor. Any recommendations on pistons? Keeping the forged crank as is.
Cylinders look to be stock bore, they may be a bit over after a good honing/cleaning at the machine shop.
