The site you might be looking for is this one: http://comancheclub.com/topic/4559-wrenches-gone-wild/
This truck started life as a 2.5 and was swapped over to a 4.0 using a 4.0 donor XJ. He used a Renix era XJ, but the idea would still be the same that you'd need to remove all of your original wiring and move each piece of the harness over from your donor. Now, it isn't totally necessary to swap everything over to make a 4.0 HO run in a Renix setup... but you won't have all of the benefits of the HO system.
If I were to do it, I'd park both vehicles next to each other, remove everything from the original vehicle, and just move one piece at a time. It everything is set in place and hooked up the way it was in the donor, you should be fine.