231 to 242 in an otherwise stock XJ

We are up to step 2.5 in the swap- I have a bezel, I have a stock 242 out of a 92 XJ, which upon looking at the date codes, has to be out of a 94 or 95...so probably a replacement unit to the 92...it is going into a 96 XJ Country originally equipped with a 231...when I raised the 96 to sauce the bolts with pb blaster, I noticed the output on my factory 231 had a half-breed extension off of the tail which is kind of a slip-yoke into case eliminator...male splines off of the T-case, which measure at 18" @ from end of shaft to front flange at trans...and have a rubber boot covering the splines...the driveshaft , after removing it, and removing the boot, slides right into the 242...3/4" length difference, but with the cherokee at normal ride height on the existing 231, actually all the way over the 3"+ of splines...so should engage far enough on the 242..I think?????...I can get better measurements and maybe some pictures if I am not bored at work and just do it tomorrow...
Question would be- what is this thing hanging out of the end of my 231...is it just something jeep did to use the same everything else with different t cases?
And on to speedo drive and driven gears? are there diffences there, or is it all through the computer?
And has anyone made sense of the wiring diagrams to the dash lights(full time, part time)...
anyone who has done this- would rather find out from their mistakes first...::