thicker head gasket such as Cometic (SP?). If the engine builder knows his stuff they will recommend a Cometic HG and surface it to that amount. However I believe the OP does not know what has been taken off to date and does not know what his starting point is. I sure can't help but I bet Seb or Bernie can. plower1 you may want to send an email to both of those guys and see if they can advise you.