Here is the MRZ Performance Lightweight pully for your CS130 GM alternator offred in the 6 rib design. Help free up some HP, not mutch but it's there... the lighter the rotational mass is, the easier the engine will rev.
Here they are, the new MRZ Performance 3100 - 3400 - 2.8 - 3.1 V6 Underdrive Pulleys! Smaller in diameter and lighter than the OEM GM pulley, this pulley will help free up some extra HP from your engine. This is the bang for the buck modification you can add to your engine and it's also easy to install in 30-45 minutes depending on your mechanical skills.