The National Hemi Owners Association did a study of Water Pumps and Housing and what parts together cool the best. This was in the 1980s I believe and all the information was put into the New Letter. They found out that the Housing cavitates in the housing behind the pump if the pump and housing are not mated. I believe what was stated is if the pump does not go deep enough to take up the room between the pump and the housing it will cause the cooling system to cavitate and cause it to over heat. There were other things that were found out. Not sure if I still have that News Letter but maybe someone else that belonged back in the 70s and 80s kept the News Letter and can post the information.

I believe the information had nothing to do with OEM casting and part numbers and what was used in each year on the Hemi.