I would like to do the exhaust on my 56 plymouth, right now it has a kind of patched together dual exhaust exiting out of the side with GM turbo mufflers on it that the Previous Owner installed. I want to put full dual exhaust out of the back with Dynomax Ultra Flow mufflers. My question is what diameter should i run? right now i measured the pipe coming out of the side it is 2-1/4. It is a stock 361 with a 2 barrel and exhaust manifolds but i plan on changing it over to a 4bbl soon. Should i go with 2-1/4 or 2-1/2?