Im on the hunt for a double water pump pully to replace the single pully I have now. I want to set up double belts. I have a single belt that runs on 3/8" pullys. My balancer has been swapped out so its already a double pully. I just need to change pullys on the water pump and alternator. When Im done, I will have two belts running off the dampner, water pump and alternator.
On another post, it looks like a double pully off a late 60's big block worked for this project (Ford #C6AE-8509-E).
I also need a double pully swap on the alternator, but I assume thats an easy after market option (also 3/8" pullys).