It has to do with what year it was built, not the displacement. Specifically, engines up through model year '69 cars had the shorter cast iron water pump. They also had a fan with the blades notched to better clear the 'bubble top' radiators.
With a fixed blade fan (or flex fan) there are a variety of spacers to position the fan distance from the radiator.
For a clutch fan, the options have been laid out above.