Here's the big deal with 348/409 engines: the combustion chamber is in the block. The inboard side of the piston comes up flush (or very nearly) with the deck/bottom of the head. The wedge-shaped area on the outboard side is the combustion chamber. The bottom of the cylinder head is flat, as you'll see in a moment. That wedge is why the deck is not at 90 degrees to the bore.