I just replaced my alternator last fall <'90 XJ Laredo> with a Napa rebuilt. I found there were 3 used in that year and the Napa store I went to had all three. I took my old one in to match it up. As I recall, the outputs were rated at 65A, 85A and 100A. All 3 looked pretty much the same. I remember one of the gates was if the XJ had AC, I don't remember the rest.
Your '89 probably had the three same choices that year too.
The 100A alternator cost $1.15 more than the 85A. Guess which one I bought? I paid $102, after handing over my core.
MoFo