No casting number on the block that I could find, but it looks like the industrial block. I apparently didn't take a photo of the pad, but as I recall it had 426 MAR on it. I don't know if these were the ones they used in NASCAR or not. I seem to remember reading that the Petty's used the Hemi block and drilled and tapped the top row of head bolt holes. Chrysler probably dropped off truck loads of parts to them back in the 1960s and 1970s.