Yes, some MJs came with bucket seats. No, XJ buckets will not bolt right in.
Configuration of the floor pan is different from the XJ floor pan, so the seat pedestals are different. However, I've compared an MJ bench seat with a pair of genuine MJ buckets I snagged at a u-pull junk yard, and it appears the pedestals are identical. I believe, and will soon be confirming, that you can drill out the rivets and bolt the XJ buckets onto the MJ pedestals.
Someone not too long ago posted or said something about having to grind off some spot welds in addition to the rivets to get the XJ buckets off the XJ pedestals. I haven't confirmed that as yet.
I know it can be done because one of the customers at my dealership had one of the techs do it for him. Unfortunately, byt the time I asked him what he had to do, he had forgotten.