Why no numbers?

I had a 69 273 block in my 65. It has assembly numbers stamped in front just below the head, but no VIN number on the oil pan rail. I think that's how warranty replacement blocks were done. It was up to the dealership to stamp the VIN and many dealerships blew it off. I don't know why your's would have neither.

EDIT: Just a guess here, but did they sell a replacement bare block? If so that probably would not have an assembly date, since it was not assembled at the factory.

In the 60's there was also a tag rivited to the front of the block behind the alternator on the passenger side. Mine did not have this tag, but I've read that they were sometimes removed during installation at the dealership.