Thanks Verne.
It was a hit or miss thing as said above. Chrysler was kind of scratching there heads on the where and how of adding the VINs to the engines so they just started stamping them across the top of the back of the assembled drivetrain. That's why you find them on the block, on the block and trans, even on the trans only in that top spot. It wasn't til 69 that the process was formalized with the VINs put on the machined boss of the block, near the oil pan.
But either way, build another block and save that one! It's too valuable to risk.