That is the only thing on the front of the engine. There is no VIN after that or on the side by the oil pan. It's cast in 72 but the "JM" I thought meant it was a 73? IDK?
Yes, cast 5-26-1972. That's close enough to the 73 start of production to be a 73 340. If there are any VIN stamps they will be on the machined head surface on the drivers side front.