I'm on Comanche number 3.
I have an 88, had an 89, and just got a '91. All left the factory 2WD and I am now picking up the parts to convert my 3rd one.
I actually prefer the 2WD ones as prices are more reasonable, and it is a safer bet they haven't been beat on.
Converting is pretty easy. I don't know about a one-day job, but it is doable in a weekend. Don't forget the interior has to come out to drill the holes/bolt in the body side bracket for the T-case shift lever.
So, axle swap, brake bleed, trans/t-case swap (or main shaft replacement in the trans) bleed clutch (or do trans fluid flush), remove and reinstall seats/console/carpet. Hope for no rust in floor, or do that while you are there. Cut hole for shifter, drill 4 holes to bolt it up, install new driveshafts.
The PITA for me is always finding an MJ rear D-shaft that is really the only MJ-specific thing you need, all else can easily come from an XJ. I had a new shaft made last time, and I'm going to see about just shortening this one this time.