Needless to say I wanted a dual setup some time ago. Local exhaust shop recommends using a transverse camaro/firebird muffler and running it long wise (instead of wheel to wheel) then have the outlet that's next to the inlet wrap around then out the other side.

Edit to clarify : I'm getting rid of the dual setup, that was done some years ago and now I'm going back to a 1:1:2 setup (I have a thing for twin tips) there's 3 of them looking at it.