[a427sc]

Lobac makes a 24" and 28", 4" dia muffler with a 3 1/2 inlet, no stub. Just cut your pipe, weld on the muffler and measure off the turn-out to fit. They will make custom internals for you with either a 1" or 7/8" inner tube, and will add extra baffles (swirl plates) if you want. Be sure to look inside the collector at the way the 4 pipes converge. Often there will be some shrouding from the way the tubes are joined.
To be really trick, use the Burns stainless clamps so you can change over to straight pipes for some extra commotion in the neighborhood.