Walker makes a 4" CAT back (or resenator back) system that is ~$250.
There are a few members who have installed this on their truck and some said that it was not a direct bolt up. Maybe Walker had fixed this problem by now?
IMO - If it requires a little bit of fabrication, you better off getting a complete 4" for a little bit more money. This will certainly save you some headaches. The Jardine and other systems can be installed in your driveway in a Saturday afternoon.