Cooling Fan Question.

[Pacecarjeff]

I have seen that all of the early Chevrolets used the short water Pump through 1968 (except Corvette = through 1972) They all used a fan with 3" bolt spacing. Now I find out from some that the 67-8 Z/28, as well as the L-78 used the later 3.25" spacing.
That is the spacing used for the later "long" water pumps.
Are the water pumps different on those 2 67-8 Chevy applications, as to use a differnt fan and clutch.

I know that all the other motor divisions used the larger spacing, and Chevy was different. Why were these 2 applications different then the rest of the Chevrolet engine line?