how are they different? 89 was the last year for the style with 2 seperate bearings in the rear. 90 on had the bearing pressed into the hub. 90 thru 92 had vented rear rotors. starting in 93 the rears were solid disks. with that change the bare stripped down spindle remained the same, but all the brake stuff, and the hub, changed and is not interchangeable.
there are basically 3 series of rear brakes
89, and 89 only..no ABS
90,91,92 all the same
93 thru 99, all the same
for the last 2 series the hub looks the same, but its really a couple of millimeters different to match the differing thickness of the center of the respective rotors. that keeps the wheel in exactly the same place.
I may still have an 89 rear spindle laying around that I could compare to a later model.