Bellhousings are not the same on the transmission end. Output shafts on the AX5/AX15 are different spline count so you need to get a 23 spline 231 or change your 21 spline 231 over to a 23 by replacing the input gear.
Google this. There's tons of detailed info out there. Folks aren't likely to recite all the ins and outs again in your thread, especially since a CJ never came with an AX5 so you are in the wrong forum.
'94 YJ - SBC/AX15/231, SOA, 8.8, 34" swampers
'06 LJ Rubicon - 31" ATs, OME 2.5", belly-up skid, other junk
'75 CJ5 - 232/T14/D20, 'glass tub w/ 2" BL, otherwise stock