Exhaust on 64 Barracuda?

You planning on dual exhaust?? Better plan on modifying your trans crossmember for the passenger side pipe to pass through or else you will to go under or flatten your pipe, neither of which is optimal. Here is a picture of the crossmember modification I was doing for members here for their early A's. I had about a dozen extra crossmembers and made them all up and sold them here, but it is a pretty straightforward mod to do, and IMO a must for dual exhaust. Compare this pic to your crossmember and you'll see what it is you're up against!!

As for the size of your pipe. I think I used 2 1/4" but I also have Spitfire headers and the collectors point straight down so clearance wasn't as much of an issue. Good luck with your project, Geof