But your dome sticks up in the chamber; that is not the issue. The question is how much below deck was the flat area of your pistons...??
I'd suspect that the OP's early 318 pistons are < .010" below deck and probably < .005". If so, the the .028" thick gasket would give a piston to head clearance under .035". Sorry... way too close for me for worn piston rocking in the bores + a bit of rod bearing wear.