Ok, Waxer and Emmetology101, pay attention here: GM used two different types of spindles. They went by the "first design" and the "second design". The first design was for spindles, hub and rotors, and backing plates up to 76. In 77, they changed the spindles and the bearing hub over to what they call the "second design". You two have got this mixed up so dont go bitching at one another. If you have an 89 K5 and need rotors from a 75 K20, then yes you would need to change the spindles. But if that same 89 found rotors from a 77 K20, then the spindles would not be required for a change. Keep in mind the "first" and "second" designs on the Chevy 4x4's. Now kiss and make up. All is forgiven!