I am soon to be reaplacing my head gasket on a 99 D16Y8..Well while I have the head off I am thinking about getting it milled down a little. Well how much can I go and stay safe? Also is the D16Z head gasket thinner then the D16Y8? I am wanting this to create more compersion and all but I was just wondering what is a safe area to stay in? Thanks for any help...