This is some interesting info i found out about the cherokee AW4 trans that you might find useful.
Pre-1991 (non-HO Jeeps) AW transmissions had 21-spline output shafts. 1991 and later units have 23-spline output shafts. At some point, the AW changed from a 0.79 4th gear ratio to a 0.75 4th...