Accurate Exhaust

I was looking at their website shopping for a set of head pipes. They claim they make them to factory specs. I called the company because I thought I saw a typo...

I have The 340 HP manifolds with the 2 1/4 outlets. So I obviously thought the head pipes would be 2 1/4 inch. The guy on the phone says the head pipes are two inch, and that they increase to 2 1/4 after they get down below the engine compartment.

Is that really how Mopar did them? Makes no sense to me to neck them down like that. What size did the 1970 340 Dart use? I'm working on getting my 360 ready for the swap.

Thanks