Finally, I have been wanting to add some safety for rear seat passengers. I picked up the seatback from a 98 ZJ to source some headrests for my XJ.
Before:
This is the headrest bracket from inside the ZJ seat. I cut this off at the bottom and cut the tube straight through about 2 inches from the bracket on each side
This is inside of the XJ foam. Interesting that it already had a recessed area for headrests. From what I read, they came standard on European and Australian models.
Then I welded the tube/bracket to the XJ seatback. Once done, reinstall foam and cutout small areas for the headrest tube to pass through. Finally, reinstall cover and cut slits for the top of the headrest tubes to pass through. Here it is finished:
Color isn't 100% matching but it doesn't look bad at all. In the future I am planning on swapping the front seats for WJ seats. I may have everything reupholstered once I do that to match but I can definitely live with these!