Rare Dodge Dart GT? Which engine is this?

Re-reading the original post again:

"Or when she was embarrassed to start it in the morning when going to work because it was so loud."

Sounds like it is actually a 340 with 318 heads on it as the OP is talking:

"I know that according to the engine’s documents that came with the car (they were lost in a house fire years ago) it said that it’s a 340 with cylinder heads from a 318."

Interesting ! Want to hear more.