As we all get older and some sicker you will see this happen its sad I know as I am just about in the same boat with health issues and have been thinking hard about selling mine.
How many RMS have you done in the past? Watch some youtube videos on jeep rear mains there some good ones see if you missed something. Also a very tiny scratch on the metal surface can cause it.
In one of my storage sheds its a pain was thinking about selling it. I used to keep it outside leaning against the shed and the neighbors cats pissed all thru it.
You are going to have to pull the head to get the lifters out on a 4.0. I would do the cam and lifters both. Check the rods for ware and to see if there bent look on youtube for some good videos.
Not sure how close the 2wd are to 4x4 ? THis is how I do them I NEVER bear on a hub anymore. I can have the most rusted hub out in under 5 Mins. Its hard to explain here's a vid its not the greatest theres better out there if you look.
https://video.search.yahoo.com/yhs/search;_ylt=A0LEVjZTlfJYRBkAPrcnnIlQ;_ylu=X3oDMTByMjB0aG5zBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNzYw--?p=Cherokee+Wheel+Hub+Removal&fr=yhs-mozilla-001&hspart=mozilla&hsimp=yhs-001#id=48&vid=f830ac289c3444381c86aa199ef00bdb&action=view
Ever try grey hound express you would have to ship at a depot and pick up at a depot it goes under the belly of the buss. I have used them a few times way cheaper and no issues here yet.
I had a friend fix it retired air force mechanic I spent two weeks on it he had it running in one day. He said it was in the main harness in the engine bay near the rear of the head. I could get a pic of the area saturday if it would help as its wrapped with black tape so I can find it. I would turn the key and couple relays would click thats how it started.
I will find out,what sucks is I just talked to him last night first time I have seen him in months. I have had him replate guns, fishing reels, lug nuts,etc over the years.