Engine ID help

Good evening,

I have a 1973 340 dart sport that I’ve owned since 1975. Im pretty sure that I have the original block and crank. The numbers on the left side of the block are 2780930-340-5. I understood that mopar used to stamp the vehicles last 6 of the vin on the block as well however they are not stamped on this block as far as I can tell. I’ve had the engine out twice, but didn’t notice anything above the pan rail. Was Mopar still stamping the last 6 digits of the vin in 1973, or had they done away with that by 73 on the less valuable cars?