Are there different calipers?

[raidmagic]

I bought some drop spindles from a friend. He threw in some rotors. I then bought a parts truck (1981) . The rotors from the parts truck wont go on the drop spindles. The spindle is too big. No big deal I used the rotors he threw in. Now the calipers bolt on without pads but won't fit with pads. Are there different calipers and if so what would I be asking for at the parts store? Is it a years difference? The drop spindles are aftermarket and I have no clue what year these rotors came off. The are about a 1/4 thicker than the ones on the parts truck. Thanks