I believe for every .020 taken off of the head it bumps up your compression 0.5:1. So if they took .040 off you'll be a full 1.0:1 compression number higher and your gunna wanna look into getting adjustable cam gears to degree out your cams. When you take that much off of your head it messes with your timing geometry and you probably be a half of a tooth or more off on your cam gears.