all depends on how much of a project you want. all of the front suspension components interchange. rear leafs are different though. everything pretty much bolts in, including the engine and wiring and dash and whatnot. please note that the 2.5L/2.8L engines won't just bolt to a 4.0L transmission. in a perfect world, I would find a solid 2.5L 87+ MJ and gut it for all of the components of the XJ.
also, welcome to the addiction :thumbsup: