Correct me if I'm wrong, but didn't the 96XJ get the dual diaphragm booster? If not, getting the later XJ booster (that damned sure does have the dual diaphragm setup...) is probably an easier mod than the ZJ job - and it's been covered in greater detail...
However, if you already have the dual diaphragm setup, the next logical upgrade would be to convert to rear disc, then use the 4 Wheel Disc master cylinder - I think the WJ unit gets used, as does a couple of Ford pieces as well (the 4WDisc mod has also been covered in useful detail around here.)
Just sayin'. No point in reinventing the wheel if you don't gotta, y'know?