I've done this, so below are a couple of notes. The writeup above is excellent, by the way.
> I had the guy at Advance Auto, where I bought my new 136 amp alt, swap the pulleys. He gladly did it.
> The alternator is secured with a two-pice bracket. When I did my swap, the metal piece metal piece also needed to be grinder. I painted the metal bracket before reinstalling. Nobody will ever see it, but it won't rust up in a day like bare metal.
> The boot for the main battery cable is keyed, so you can either use the old one, as mentioned above, or snip the little plastic tab off like I did.
Replacing the alternator on an XJ in kind of a PITA anyway, so if you have to do the chore you might as well upgrade the alternator. The Mean Green alt is nice, but is a solid $400. A 1998 Grand Cherokee V8 136 amp unit is a much better buy.