On my 2010 6.2 I removed stock muffler, ordered a xr1 borla muffler, 3.5 in 3.5 out, removed the two nuts that bolted the exhaust together after Y-pipe and just flipped the pipe over and rebolted it back up. This made the offset in the factory muffler be more of a straight shot out the back of the truck. I then added a short piece of 3.5 inch pipe before xr1 and welded xr1 directly to factory exhaust behind xr1 and it looked factory but sounded pretty darn good. Never had any issues!! If your gonna get a tune then you can do whatever you want with the convertors because tuner can tune the rear O2s out and turn off codes. Well at least you can in AL we dont have to pass emissions. But you could still remove that rear one Im guessn with no issues I would think.