1972 Demon with 71 340 casting

That is not what you go by to tell if it’s matching numbers. It should be cast in 71. I think on drivers side of your block right above your oil pan is a flat pad. It will have your sequence number which is the last 6 digits of your vin. That’s what you go by. If not on drivers side it’s on passenger. Pretty sure drivers. That’s pretty early though.