i have a dual exhaust on my truck that is only custom AFTER the o2 sensor. on each side, it goes cutout, highflow cat, 8" glasspack. then it runs out the back to some big tips. my truck gets dyno tested for emmissions, and my mechanic says as far as sight goes, as long as theres a cat and a muffler, its cool by him. doesnt matter what kind of cat and muffler they are.

when i finally put on my long tube headers, i wanna get it set up so i can have my o2 sensors right after the collectors, then do electric cutouts inside the frame rails, and then have the pipe bent up to go over to the outside of the frame rail (running tight and parallel to the frame rail), then do cat, glasspack, and have it bent out 45 degrees with my big tips right before the tires. that way i can eliminate a bunch of extra pipe and make room for a big hitch in the back.