The part # for the '89-91 Ranger is different than for the '84-88, so I'd be wary of getting one unless you can see and measure it yourself.
They're different part numbers because the '89-'91 is a 2 piece design. Theres a hub (dis ignition: hall effect trigger wheel)that the pulley bolts to. You grab the hub & pulley and install it as a unit it should work just fine.