I have those heads on my hemi. Makes somewhere in the 850 hp ballpark on motor only. They are CNC ported by MCH and max intake flow was 429.1 cfm if I recall correctly. I've been running them since 2006 w/ no real issues. I was worried after hearing about dropped seats from some people, but no issues w/ mine. twocents

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax