The beauty of going with a single in/dual outlet muffler is that you can position the muffler side to side to match up with the existing pipe coming back from the cat. You have the room so it doesn't have to match up exactly.
Once you take a look at your stock muffler you'll see you have a lot of room to play with there.
New tailpipes would be in order of course.
I went with the 18" oval Magnaflow unit, single in/dual out, and it sounds great.