From what I understand, any jeep with a D30 front end. I know all xj axles will work, and if you get them from a 94 or newer, there is a bigger u-joint in the shaft (x-297).
Also, do you have ABS? In '91 I think they still had the disconnect axle for non-ABS and a solid axle for the ABS version. Although many people like to swap in a solid axle with the stonger 297 u-joints (I plan to do this)
I'm thinking that the disco or non-disco axle is a function of which transfer case is installed. My '87 with NP242 is non-disco and my daughter's '89 with NP231 has a disco axle.