[BritishGreen68]

make sure you use metal etch on the bare metal block before other topcoats. epoxy doesn't adhere all that great to rough cast metal because you cant really sand it properly for a good mechanical adhesion. Or...Tape the top surface of the block off when you paint so its bare metal out to the edge and the head doesn't contact the paint at all, and deal with a little bare metal area around the head, or assemble it unpainted and do a tight mask job on the heads and spray it with them on. or you could set the head on the block unpainted, spray some paint or something around the OD of the head so you have its exact profile on the block deck, and mask on that line and trim it perfectly on the head line so the head wouldn't touch the paint but it would be up to the edge of the head.. you might also have too thick of a paint build up, and it will be prone to cracking no matter what,.. thats all i got lol..