Not hard at all. One weekend should be fine. A 91 can probably get away without an SYE for a while, but it's something you want to do for sure. Soak all the bolts with liquid wrench or equiv. for a few days prior. One thing to watch is the front leaf spring bolts. Sometimes they can be pretty rusted stuck. It's possible to break loose the nut that's welded to the body, so watch for that. And naxja.org is a good place to go for install help, lotsa good XJ tech there. Have fun.
More then likly you will have to do the SYE ASAP, but you could lower the T-case, if it is the short "bad and ugly ride" arms. I have a TJ with the RE long arm on the front and it took four days, BUT I could have done it in one or two. If I worked on it all day the first day.
You can pull the slip yoke off of a '96+ XJ and attach it to your driveshaft. The 96+ slipyokes are the 'long travel style' that have more room for the ujoint to move. I ran this on my XJ with 5.5" lift with no vibes and no problems off road either. Anything over 5.5" and you will need a longer driveshaft. The SYE is a good choice either way because it adds beef to the main shaft (if you get the HD version).
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