I had the same problems when I converted over to 4wd. I just decided to go with a whole new AW4 though. But then I was using a YJ t-case, so I'm not sure if their shafts differ with an XJ t-case shaft...
I ended up using a matched AW4/231 combo that came out of an 87 Wagoneer XJ when I did my conversion. I didn't think the internal transmission work was worth it, but I was dealing with a 2WD box that already had 270,000 miles on it.
The part numbers are for the 21 spline output shaft. The adaptor and seals should be the same though. My parts book is for an 88, so it works well for me. I didn't even think about the later change.
As sick as it sounds, I have been looking into converting my 89 wagoneer with the aw4 and 242 t-case into a 2 wheel drive jeep. If you would be into swapping parts just reply to this.