2wd to 4wd conversion

I have a chance to get a XJ for free. It is an 88 4.0L basic equiptment. It is only 2wd though.
I also have a friend that owns a used car dealer and he offered to get me a wreaked XJ at a salvage auction cheap.
So, the question is, is there anything I should know, look out for, etc. before attempting this?
I have a shop, tool and have been a mechanic for 14 years. I have tons of experiance with modifying and building stuff. So, its not a matter of "how hard or can I do it", but is there anything that Jeep did different between the 2 and 4wd XJs?
I know the front axle is basicly the same without the diff and axles.

What is the advantage between the 2 T-cases? I know the NP231 and NP242 were offered, what is better?(If I have a choice)
One more advantage to the 88 may be that it may have the tow package and the D44 rear.
Any help, suggestions would be great.

What year and what engine is the prospective "donor"? If it's an '86 or older, it won't have the same transmission or transfer case as used with the 4.0L.

As to transfer cases, the 231 and 242 are close in strength. The difference is primarily that the 242 has an additional operating mode -- "full time" 4WD. This uses a differential within the transfer case to (ahem) differentiate the front and rear drive shafts so you can drive on dry pavement in 4WD without binding up the drive train. The 242 is slightly weaker than the 231, according to New Venture Gear's web site, but lots of people wheel with 242s and they seem to survive.

Keep in mind that unless the donor vehicle has the same gear ratio as the 2WD vehicle, you'll have to either regear one end or swap both axles from the donor.

I am looking into a donor Jeep that is a 90. I know that I would need a I6 donor to make the trans and T-case work, and I know about the gearing, matching and all.
What I am wondering about is, are there any brackets missing or extra that need removing, any irreplacable things that would make this swap impossible.
I just need to know if what I am going to attempt is just a very large bolt on project, or if it is going to require major fab work.
Anyone ever done this or seen it done?

I'm just about done converting my MJ to 4WD..all I have left is the front axle install (as soon as I find a 4.10 D30 ) It is almost completely bolt-on. All of the suspension parts bolt in the same stock locations, and the holes for the transfer case linkage are stamped into the trans tunnel, just knock them out.
Couple little things to keep in mind-> You'll need a new rear DS or have your 2WD one cut to size, and a longer speedo cable from the 4WD (unless it's electronic). You'll have to swap the vaccuum harness into the 2WD unless you have a non-disco axle, or you could rig the vac motor, or replace the 2 pc shaft with a solid shaft from a non-disco axle, and add an inner axle seal.
All together, I've spent about 3 days working on it, with about one more to go to get everything finished, but I took my time and did some extra stuff along the way (resurfaced flywheel, new rear main seal, added front engine and TC skid, etc.) Shoot me a PM or EM if I can help ya with anything else.
HTH,
Jeff