340 casting production

That means that all leftover parts were sent to MOPAR replacement parts or to the Mopar Performance outlet. Blocks with #'s and casting #/s could have come into the market many ways such as a SS racer needing a new block.
The only difference that I know of in the 72 and 73 engines was that the 73's had the cast crank. Just my opinion but I still think the 340 is in a leauge of it's own.
Wish I had 3000 of them.