I just did P/S pumps on both the 90 XJ and the 88 MJ, same part. The only difference was the pulleys.
My MJ has a metal pulley, with no spokes or holes, and mounts flush to the end of the pulley shaft.
My XJ has a plastic (ABS?) pulley, it is spoked, but the spokes don't go all the way through. The pulley mount is recessed, about <1/2" flush with the shoulder inside. I also replaced the pressure line (and o-rings) and the return line.
The return hose on both was a moulded piece, metal lined. I replaced it with bulk rubber P/S hose. My fluid on both was nasty. I've put "flush P/S pump" on my annual maintenance list.