The front stamp is the engine 'serial number'. It was stamped when the engine was completed.

After completion, it was readied to ship to an auto plant with other assembled engines.

When a car was coming down the line, an assembled engine of the correct type / application was sent to the main line to be installed in a car.

Just before the engine and transmission were mated to a car, the VIN stamps were done.

Car 'build dates' were not recorded back then.