Is this an oddity or just Mopar weirdness?

So your 340 came out of a 70 Dart, but was built in Late 71 for an early 72 car..... sounds to me like a previous owner of the 70 did a motor swap sometime in the last 45 years or so..... was the 70 a real 340 car? Is it a warranty replacement from back in the day? Did a previous owner just have too much fun building what he wanted?