What to tell the exhaust shop.

Factory your 63 will have a one barrel.You can make (or maybe find ) a one barrel to 2 barrel adapter.Not the best option. Or, Chrysler did make what was called a Super Six 225 that was a factory 2 barrel. You may want to place a wanted post here. Someone may have one.Last one I had I sold for $50 it was cast iron. I would say expect to pay that or $100 or more.Parts prices just keep on going up.