98XJLongbuild, It doesn't sound or should I say look like you did any research.
As stated before me doing a search will give you the answer to your questions.
Yes, ARBs, gears, diff covers, upper and lower brackets, this that and the other thing are all availible for these axles.
As for a vaccum disco, I wouldn't use it! It is just another weak link in my opinion.
I also wouldn't hack up a good running full size.(though you didn't say if it was running.)
I run 44 front and rear under my XJ with 4.88s, lockers, alloys a 3link front and 4 link rear.
Anything can be done. Mine is about middle of the road. There are tons of rigs bigger badder and better than mine out there.
I did about a true year of research before buying a single part for mine.
Read a lot then ask if you don't find the answer.
I would love to see pics of both your XJ and the Waggy and the progress.
Good luck,
Stukboy
PS: I'm not bustin balls just my observation. No offense I hope!