The Edelbrock, Stealth, Pro Comp, etc., heads all need to be gone through by a machine shop before being bolted on. The Trick Flow heads aren't even available yet.
Todd Marsh has the Sidewinders he sells already checked out and any issues corrected.

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 4 speed, Dana 60
'71 Demon 340, no drivetrain, on blocks behind the barn
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax