Just typing this up in case it helps anyone in the future! The clutch on my AC compressor wore out and stopped engaging–time for a replacement. Yes I could have just gotten a whole new compressor but my system is charged and holding refrigerant perfectly so I didn’t want to mess with that. Also the new clutch hub is under $25! (I ordered it from Autozone: https://www.autozone.com/cooling-heating-and-climate-control/a-c-clutch-and-components/p/santech-mt2336-gm-a6-short-shaft-clutch-hub/607250_0_0).
Removing the old one was very easy (I used O’Reilly’s AC compressor rental kit: https://www.oreillyauto.com/detail/c/evertough/rental-tools-evertough-air-conditioning-clutch-tool/ren1/67100/v/a/631/automotive-car-1989-jaguar-xjs?q=Rental+Tools+EverTough+Air+Conditioning+Clutch+Tool&pos=0)
I did not have to unbolt the compressor at all to get the old clutch hub off.
Install was much harder. First, I needed a new square key (4mm sq. x under 20mm long) because the old one came out with the old clutch hub and was beat up and seized to it anyhow. A 20 cent part at any normal hardware store! Next, try as I might I could not get the slightly longer install tool in place to press fit the new clutch hub on. Off with the AC compressor’s 4 mounting bolts (unbolting it was way easier than I feared). Note it is HEAVY when it is free so you really have to wrangle it around. It can be tipped up on its back end though with the pulley facing skyward. That’s the best angle to install the new clutch hub. The press fit is tight–very tight. I didn’t want to damage the rental tool so I decided when it was not pressing it on any further to go for a bigger tool. I used my 10 ton pulley/rotor/drum puller and it worked perfectly. The square collar on the AC compressor is a strong place to but the jaws of the puller and basically effortlessly it pressed the new clutch hub into place.
I tried a few different clutch gaps (manuals and online gave me varying numbers). I ultimately settled on 25 thousandths. At this gap there’s no danger of rubbing when the clutch is disengaged and no slipping when the electromagnetic comes on. A few places online people suggested 30 or 35 thousandths but this is too much in my opinion. My clutch chattered over maybe an eighth or even a quarter turn before properly engaging at that gap. No need to make the magnet do more work than it needs to!
Anyhow I hope this helps someone get their AC going again. Happy to answer questions if I can be of help! This site has given me a lot and I don’t think I’ve seen a clutch hub write up in the forum so here you go!