4-Door with 340 from the factory?

My son's 1967 Dart GT convertible looks very factory (440/4sp/Barracuda dash). We can tell who knows and who doesn't by their reaction when looking at the fleet car fender tag. Unfortunately I'm never around when they go ape over how "rare" the car is. It's my wife that gets to try to explain it to them. They always say that she doesn't know...