88-98 c1500 spindles

i know the 88-91 has 1" rotors and the 92-98 has 1 1/4" rotors but why do some companies have 2 or 3 different spindles for the 88-91 regular cabs...AIM has one for the work truck and the silverado but yet i dont see that with beltech or djm....what do i need...91 regular cab c1500....originally a work truck.....4.3 v6...any help would be appreciated ...