1973 dart sport 340 (factory 275 horsepower)

Look at the front of the block, just below drivers side head. There should be some number/letters stamped there.

Just because the block was cast in 1971, doesn't make it an early build engine.

Exactly, I had a cast date 1971 340 block but when I checked the numbers n the front of the block it was built in 1973.