I have seen and wheeled with two XJ's that were coil sprung in the rear.
Both sucked big time compared to a stock set up. Off camber can be really bad, unless you use sway bars front and rear (defeating the purpose of creating flex).
There was a kit produced in France that allowed colis to be fitted in the rear of a stock Cherokee - but I don't think it is still available. AFAIK, Tomken's kit never made it past the prototype stage - offcamber stability being a large problem.
Yes it can be done, in my opinion though, you can spend your money modifying your XJ far more effectively.
Now if you are building it to race Baja style, that's a whole different story. you can also try NAXJA.org and ask there. One of the guys I wheeled with with the coil sprung XJ used to be a member. I think he went by "Brian from NM" or similar on the board.