I'm the water pump pulley king! I know more about water pump pulley's then anyone should ever know! Just kidding. Sixstarved sent me a link to a site that had all the part numbers, pulley diameters, and bolt hole diameters for all 1st Gen Firebirds scanned from the original factory shop manual. It even had pictures to point out the different pulley arrangements with numbers for different pulley combinations. It was VERY helpful. The link is:
http://1968firebird.org/illustrated/pullybelt/pullybelt1.html