if you were going to do that, I'd just do what I did on my 5th ave--run a big single-- I've got 2.5" off the headers to a flowmaster Y, and into a 3" muffler, and 3" over the axle. you can fit up to a 4" pipe along side the tank in a big single config. but finding (and fitting) enough muffler volume to keep things tolerable gets hard to do.