I had documented the fan and some other package detail on my car's page a few years back. http://www.abilitypc.com/photos/firebird/

I haven't updated it, and it does not contain part numbers, so I should make a comprehensive chart for the site. Thanks for the '68 info, I have the '69 and '67 info and will put this together when I have a few minutes.

If you buy a used fan with a silicone clutch, try to buy it right off the car or engine. If it's been sitting flat on a bench or shelf for a long while the silicone can seep into the bearing area. Vertically stored with no sign of residue, moisture, rust or damp dust should be okay too. Best bet would be to put a new clutch on a new or used fan, and be sure to check any used fan for straightness as well. A glass tabletop or granite countertop is a good surface, all blades should touch the surface at the same time. Vibration from a bent fan will quickly destroy your water pump bearings.