I also found this magnaflow muffler. It is not an x-pipe but a dual 3"in/out straight through design. You are right about the dimensions in the drive tunnel. You can actually replace the x-pipe with a mufflered x-pipe and still have over 2 feet to place a second muffler if you wanted to, so space isn't an issue.
http://www.magnaflow.com/02product/s...e=main&id=9074