The MUTCD specifically depicts the four-lens layout in Figure 4D-3, G. As AC said, this would only be acceptable if the green ball/arrow were followed by a yellow ball. If used as a leading green, a yellow arrow section is required.
Virtually every fire truck is different. Pumpers tend to have the same characteristics as Single Unit but are longer. I agree, the best bet is to contact the fire company where you are working. If they don't have the vehicle specs, they may be able to give you the manufacturer information.
