In the old days there was a standard o-ring size/location on top of the sleeve and then a matching receiver groove in the head. You are wise to try to follow a standard path. But nowadays it seems everybody wants to be different and it makes things a lot harder. I had a new billet Pro Mod Hemi in the other day that had the old, old way of oringing the heads. It drives you crazy. Try to find out the closet thing to "standard" and go with it.