Quote Originally Posted by camaro_fever68
420+cid will be head limited with anything under 227cc runners. Not a bad thing if you're using a GM 400 block though. I figured a 6500rpm redline and that would be a perfect combo of parts on a 410/412 short block. You could back down on the gear and go with more tire though and use the torque of a 421cid to pull it. You'll most likely run out of head by 6000rpm.
Good call Ray.
I would also say a fully CNC'D 23 degree head will support up to 650 hp in a natually aspirated engine after that I would be shopping for a set of 18 degree heads.