FYI Update I received an answer back from Dynomax. I just asked basically what I asked here. What they recommend for pipe size and what muffler. Here is their reply. I find it funny they can design a muffler but have no idea the recommend sizes for what they design. Maybe this old stovebolt is just to old for them lol OH well. One down and one to go with the muffler manufactures.

Thank you for your inquiry for Dynomax Exhaust. We appreciate your interest in our products. I am sorry but we do not do pipe sizing for custom applications. The pipe sizing is done by the engineers for stock cat back system applications. You would want to contact a performance exhaust shop to help you size the pipes correctly for your application.

"As I lay rubber down the street, I pray for traction I can keep, but if I spin and begin to slide, please dear God protect my sweet ride." -Amen

56 Chevy 3100