Dont even bother with the heads or cam if 600 rwhp is your goal. I honestly wouldnt even touch the high side. Lt4 low side pump, p1x, single nozzle m15 meth kit, usual bolt ons, and you are over 600 rwhp.
Heres the results my p1x build got me....
https://www.camaro6.com/forums/showthread.php?t=565560