[Blackcat]

Ryan,
The 64-68 water pump housing had 2 plates inside. It is critical that they are not really rusted. This will cause the water to get around the plates and not cool properly.
Also check the housing for rot that will allow water to bypass the plates. Check the waterpump. Make sure that it has a cast impeller that the blades go to the center. DO NOT use any one with a stamped steel impeller!! You may have to check several pumps untill you get a good one. It would be in your best interest to powerflush your cooling system. Have your radiator rotted out. If it is in poor shape. Replace it with a new 4-row. Buy the repro fan shroud.
It will make a big difference.