The starter to be used is determined by the engine to bellhousing adapter that is used. The 89-93 starters are different from the 94 up one and are not interchangeable. 1994 was the first year the NV4500 was installed behind the Cummins. The 4500 bellhousing adapter starting in 1994 is thicker than the earlier ones and the starter bolt pattern is different. I bought an adapter bellhousing which uses the early pattern 5 speed engine adapter to bolt up to the NV4500 transmission (and uses the early pattern starter). I would need to measure the thickness between the 5 speed & the auto engine adapters before I could be 100% sure they are the same in the 89-91 automatic series. I think the 94 went to the thicker adapter in the automatic when the lockup convertors were first installed.