With and angle grinder, welder and a pair of new perches the XJ can be made to work quite easily. I imagine the grand can too, but there'd be more stuff to cut off.
A popular upgrade is a Ford 8.8 out of a 95 (?) and newer Explorer. Stronger axle, same bolt pattern, disc brakes. it is a bit narrower, though, so you might want to run wheel spacers.
If I remember any of this information wrong I'm sure someone will correct me.