No way on a 5.9 I6 diesel in XJ, gotta see pix to believe that one. I've personally seen a 454 in a xj. When I talked with the owner, he said in order to get a huge radiator in, he had to move the firewall 9" back. The bay got widened 6"
it has coil overs.
Now a 4BT 4cyl cummins in a xj is possible, 5.9 no way.

The XJ is a pile when it comes to strength, there is nothing strong about them. Until I beefed my with frame stiffeners and intigrated sliders, if you twisted it up the door would not open.
Please don't compare a rig with a frame (even an old CJ) to a unibody. That is a joke.

SD