drain89,
Another possibility is a pulley from a 65?, it's stamped steel and is part #9781741 from what I've read this is a direct replacement for the cast aluminum pulley. this info comes from another Pontiac enthusiast - pfilean.
here's an ebay link for that pulley. have the seller measure the outside OD to make sure it will fit inside your harmonic balancer.
https://www.ebay.com/itm/28573539522...QaAp54EALw_wcB