Ummm. The serpantine pulley came with the alternator. The alternator was for something like an '87 Suburban with the towing package and all air and stuff. It is like a 95 amp alternator and is the small housing. Bolted right up to the brackets and are the same for a big block or small block. You could easily get the pully from GM as it is the same for SB or BB. the other two pully's are different though. Good luck with the swap. It totally fixed a squeeking, belt throwing problem that I had.