That may be trcky... I think it was GJ who had tried about 5 different pulleys till he got the right one. But I hope you only need a basic one...
If you assemble everything loosely, check to see if you'll need a single or double groove. Then there are different diameter pulleys, but you should be able to make most any of them work...
Check with Quenton, in Chatsworth, or Jim C who is down in San Diego, but in in the Pontiac Club and will have lots of contacts Jimc2002@aol.com
Wade in LA may have something laying around? But I think he has transplanted another brand motor in his 69, so maybe he wont?
Or Firebird Bill - Bill Edmunds EarlyBrds@aol.com He may have one and could get it to you in a few days...
Or even Terry in FL. He should have one and could get it to you in a few days. youjincho@prodigy.net
Hope you get it figured out, and or hope you find your original!