It could just use different part numbers because they are designed for different vehicles. The control assembly between the vans and trucks themselves are identical, only difference being that on the vans with dual fuel tanks, there was a completely seperate selector switch, whereas on the trucks it was on the right of the assembly and the Bronco's used them for the rear window switch. Hold up an assembly from a single tank truck with one from an Econoline, there will be no differences, or at least very minimal.

Edit: If you look at the assembly numbers in the above pictures, the switch assembly is #19980 in both.