As for your block, I don't think anyone can say with definitive authority that every single block was stamped on the distributor pad. That was indeed the practice up through at least 55, but can any say for absolute certain? I am not sure that they can.
I think it would be VERY rare to have a pre 1957 engine get out of the factory without having a stamped serial number as most State's used this number for title identification.
Mike B
