On my 2000 XJ, I had a Custom 4x4 Fabrication bumper and tire carrier. It was NOT a tow point, so it only mounted in the stock location plus four bolts (two on each frame rail) on the underside where the hitch mounts. Personally, I was in favor of using my Hidden Hitch as a tow point rather then a bumper.
http://www.custom4x4fabrication.com/rear_xj.html
A few things I liked about this design is that the tire carrier mounted to the face of the bumper instead of the top and the tire was centered. This kept the tire lower so I could see over it and out of the corners so I could see around it when using the rear view mirror.