The shaft is 3/4" on a truck vs 5/8" and a different length. I don't know which is longer but the pulleys also have a different offset, to match their respective pumps. Belt positioning is the same as long as the pulley matches the pump.
I don't know if there was some engineering reason for the larger shaft diameter but for how the trucks are typically used today, a car pump and pulley combo works perfectly fine and will be easier to find. Although the car pulley diameter tends to be larger, which can contribute to overheating in some scenarios or regions.
Lawrenceville, GA