How thick are those head gaskets?Fel Pro top end gasket set
#hs7733pt16
Wild Guess: Given that the pistons are ~.025--.027 in the hole, those gaskets are too thick for proper quench/squish.
When it was me, I had the block zero-decked--cut .025. Looking back, I should have had the block cut .015 and used a thinner head gasket.