Finished the exhaust up. It is using some thin wall pipe I found laying around that is about 1 1/4 OD. I used the stock resonator and the best muffler I could find out of my collection. I had to make two bends in the pipe to fit the whole thing together. It is exiting right through the back mesh panel instead of under the bumper. I didn't want to deal with a hole in the underbody cover so this way it should be fine. It might get the spot in the mesh dirty but it is just metal so it won't hurt it.
I still need to make up some random brackets on the rear suspension and back end but nothing major. I will also have to slightly angle the tip of the exhaust to make sure it doesn't get near the bumper plastic then paint the muffler flat black to keep it hidden. I also found out that the exhaust pipe that was on the XFi was split about 2ft long right after the manifold so it was maybe 2 inches away from the oxygen sensor and making the car think it was running a bit leaner than it really was so it was actually making it run rich.
After putting the exhaust on the only thing left was to put some gas in it and hook the battery up to see if it would start. The car started second try but would only stay running when the starter was engaged. It took several hours to track down the problem and it was a ground wire not connected under the hood. After that it starts and runs perfectly fine.