The '86.5-87 calipers are different from the '88-91's. The smaller piston is larger in those later models. Also, I'm pretty sure that the dust sealing system is different on the '89 and '90's, fom the '88's, and different again on the '91's. The '88's, 89-90's, and the '91's all have different part numbers in PET, as I recall.

Gary Knox
West Chester, PA