Hey if that is a factory 1968 318, that will have the Valve Relief Flat Top pistons in it 9.2:1 compression right out of the factory in '68. Made 230 hp even with the 2bbl on it, put a 4 bbl on it and wake it right up.
I would be interested in those stock bore valve relief pistons if you really want to stroke your block. Thanks . . .