Why would the wheel base make a difference on what fuel pump to use?

 

Yeah. And why would a 1956 312 require an external fuel filter?

Tank capacity, location, length of fuel line, dual tank configuration, valve and gauge switching, fuel reservoir present or not. There are multiple reasons. In addition the engine will likely use more or less fuel over time than others.
Could you be more specific?
tom

 

1999 Ford Ranger. 2.5l engine
I would think the tank size would be the same for a short bed or a long bed.
126" wb or 112" wb doesn't seem like it would matter.

 

it does matter my short bed tank was only 15 gallons my long bed is about 19 gallons,,,