If more compression is your aim, and doing it affordably is much of a factor, then i would mill the heads. I did exactly that on my eddie heads a few years ago to up my compression about the amount you are wanting to do on my old 416 motor.They were flattops 5 in the hole.

The fact is, if you cut them and even decide down the road to build a different motor using those same heads, just spec the NEW pistons to where the new milled heads would be chamber wise..
Otherwise you have new pistons, rings, balancing, etc, involved in just wanting to raise your compression..and most likely everything else, mains, rods, etc if you have it completely pulled apart anyhow.

Milling the heads just involves head gaskets/intake gaskets and an afternoon in the garage.......and will net the desired result.