340 upgrades.

The J heads are (mine are) 72 cc large. With a zero deck piston, the ratio works out to be 9.8-1 with a .039 head gasket. I used KB 107's @ .030. They have ample valve relief. I had a .500 lift ccam in there with booooo-koooo room.
Though this ratio is a bit high for the cam mentioned, a Fed-Mougal piston is also good being a slight below zero deck.
I *Think* it was .010 down the hole. Also has deep valve reliefs.