MJ's have a foot more wheelbase over an XJ so rear shafts do not interchange.
nothing in your MJ will help the 4.0 to function. it ALL needs to be swapped, including the radiator and rad support (which necessitates swapping the hood and latches too). it's been done. :thumbsup: oh, and you'll need to splice the XJs rear lighting wires into the MJ harness and the aforementioned fuel pump and whatever changes to the lines it might need.