Guys, the reason the casting number is the same, is when they developed the Xblock for racing, they modified the already in use core boxes, and didn't bother to change the numbers. The blocks were rough bored to 318 bore size, and had filled in pan rails, thicker decks and wall thicknesses. And a big freaking "X" right up by the dipstick area. The engine in this discussion is a plain old 318, nothing special AT ALL