Over the past two weeks I have been involved with the replacing of two new, not rebuilt, short shaft water pumps and installing new fan clutches on sbc's. Parts came from two differtent dealers, one was Napa, and each time the bushings in the fan clutch were 1/8 inch or more too short the catch the shaft of the water pump. This left the fan clutch off center on the water pump. Checked some old clutches and the bushing was 3/4 in. long and flush with the outer housing of the clutch. The new ones are 5/8 in. long and are recessed about "1/8 to 1/4 inches inside of the fan clutch housing" and it won't catch the water pump shaft.
cw