69 Dart/Barracuda 340/383 tail pipe size?

the Accurate Liimited tailpipes are 2 1/4 unless you ask for something else.

IMHO if you want something smaller it would be more straight forward to just stuff a rag up the tailpipe
I have to disagree with that regarding stock or close to stock builds. Although I would probably use something larger "just because" that's what "I" would do. lol