Here is a pic of the two pumps.
The large shaft water pump was used on heavy duty trucks. The bigger shaft allows for use of bigger bearings which are necessary because the HD trucks often have two belts which are also bigger than the pass cars. This puts vastly increased loads on the bearings. The HD pump has extra gussetts cast on the snout to carry the bigger loads and the snout itself is bigger. There is likely to be more pumping difference between the various designs of impellers than the HD and standard pump as originally delivered by FoMoCo.
Because the casting is different between std and HD it is unlikely that ReBop has built aluminum HD pumps but Frank can confirm.
Doug T
The Highlands, Louisville, Ky.
