My car, produced second week of December 1968 at the Lordstown plant, uses the short hub (4") water pump. Although the pump has been exchanged several times over the years, I am pretty sure that the pulleys, brackets etc are originals. Even if the long nose pump was introduced around mid 69, it seems that there were old pumps still being used at the assembly line.

As for the clutch fan vs flex fan efficiency, I've tried both and my personal experince (which is not by any means scientifically proven...) is that the flex fan performs better at idle or in traffic, clutch fan keeps engine cooler at highway speeds.