My take: The XJ is a great rig when kept within it's capacities. I'd keep one at 33" or less tire, 4" or less lift and run the 4.0L and 231 into the ground and start over with another, uncracked unibody version so you can swap all the lift/axles/tires/etc onto the next one.
If you insist on ton axles and 37" or larger tires, I'd go with the K5. I like the TBI versions personally, but any small block version will work fine. I think the K5 is a bit big for serious trail work but there are a LOT of them out there in various narrowed forms. A built K5 will take on any Jeep Safari trail without hesitation but the size/weight will be an issue. I think a 37" tire version of a K5 will do A LOT of good trail runs and offer room an XJ can't even dream of. The compromise is size. You'll love the size and hate it at the same time.
Not a K5, but it's Dodge equivalent and a crack free (at the time) XJ with some bonus tube. Picture from '08?
The RamCharger is still going while we've all morphed to other rigs. He's got a ton front axle and some semi-float 14 bolt or something in the rear now. Why it's not a cool kid 14 bolt, I don't know.
The RamCharger hauls about the same amount of gear I have stuffed in my silver Jeep but the RamCharger has it all in a single box that's easy to strap down in the back and is readily available. I have gear stuffed EVERYWHERE in my silver "Jeep" but it works for me most of the time. The only modern comparison to an K5 (or Bronco or RamCharger) is a JKU. The RamCharger has a serious "pucker factor" when we get into trails like Pritchett and such. High center of gravity, MASSIVE hood and tall leaf spring lift make it "interesting" on the trail. Rick tolerates us pretty well and we've put him into some spots I'm not sure how we got him out of. If I built a K5, it would be similar to the RamCharger pictured (less KC lights for sure) but less lift and more cutting. I don't know that I'd use it for true "rock crawling" as much as I would just a good trail vehicle I pull my lunch out of easily.
I like the JKU for trail riding much more than the RamCharger. Way less pucker factor. Similar cargo space, same seatbelt amount, a little better fuel mileage. Rick's had the RamCharger on the trails with us for at least 15 years though. He's definitely got his $ out of it.