i need a little 340 help. Lets Talk head gaskets

That’s Big Ole flat dome (reminds me of what you would see in a two stroke motorcycle engine) sticking out of the hole. Can you get a physical measurement of how far above deck the piston is on the valley side and the outside of the block? That combination is almost begging for a set of properly worked 974 (E58 hi po and some industrial 360s) heads with 11/32 2.02/1.60 valves.