IO'm running a single sprot-truck right now with dual 2 1/4 inlets, and a simgle 4" outlet. One thing to watch out for is clearance between the frame and drive-shaft. There's not a whole bunch of room.

I'm gathering parts for the next exhaust mod....Thorley headers, 2.5 dual pipes with an "X" pipe, dual spintechs, and a single 5" tail. Oh yeah...No cats. My fourth set is starting to break up. Only 23k on truck with no towing. Until the factory can figure out the cat problem, I'm not running them.