you would of had to really gouged them and it would not have any thing with blowing the fire rings out? i cut many heads and blocks on my mill. i think your deck is not flat or the heads or both and if you say there are flat how do you know ? how did you check them ? and were they check for twist and like i said many chevy decks are very choppy .i have use stock fel-pro head gaskets with alot of cr but every thing has to be dead flat