the numbers you want are on the back of the block on top, right behind the drivers side head. the front pad numbers are on the pass side where the front of head meets the block . the rear #'s will decode what block it is, the fronts will tell ya what it came from. if the fornt numbers are not there that means your block has been decked .alot of guys here run factory ovals with upsized valves with good results. pull a valve cover,and find those numbers between the rocker arms . numbers ending in 781 or 049 are the most popular ones ,but there are others that will make good power as well. it would be nice to know exactly what you have to work with before you proceed, ya know.