Earliest 340 production date/number

I knew it'd pay off to search for this thread instead of start a new one!Anyways,I was digging around through some of the blocks I still have and found a 340 dated 6/21/67.After reading these posts I realize it's not exactly rare to find one this early,but I couldn't find a VIN stamped into it anywhere.Not even a machined pad to stamp the numbers into.It makes me wonder if this was a factory replacement block or something along those lines.Anyone have any ideas on this?