In my 2000 XJ I have an np231 transfer case I just so happen to have a few extra 231's and I also have an np242, if I were to be inclined to put the 242 in my xj. Would I have to do any other modifications. (I.e. - axles transmissions drive shafts etc.)
Also, I have noticed on my transfer case that I have an electronic connection on the rear at the top... on my older spare 231's it appears there is a vacuum connection instead of that electronic connection... are these interchangeable, what are the functions of these two different set ups?

 

they both come in 21 and 23 spline variations i would check to make sure the splines mates and the input length is the same and you should be fine. as for the connection on top it may have to do with the older CAD dana 30 but i don't know for sure. other than that and linkage i don't know of any other issues in switching

in my opinion i would stay with the 231 they are stronger and easier to rebuild than the 242, plus more aftermarket support.

www.navak-adapt.com has a ton of info on both t-cases