Not certain, but I think some of the police or "fleet" duty XJs may have come with a bench seat. They would have had to be modified to use an MJ foot brake because there isn't enough room for a hand brake in the little notch at the middle of the bench.
If you are willing to modify the brake, an MJ bench will bolt onto the XJ seat pedestals. Several people have gone the opposite direction, converting MJs to XJ buckets by swapping the seats on the pedestals.