Those are heavily modified P2V Neptunes, served in Vietnam in "unofficial" clandestine roles. The only official gunships were AC-47s, AC-119s, and AC-130s, but there were a number of other aircraft that were modified with guns and heavier weapons, like the P2V and the A-26 Invader. Generally they were real-echelon aircraft that were WWII or 1950s leftovers, some were put on the Air America roster and took off from bases in Thailand or Vietnam, to conduct bombing or clandestine runs in Laos or Cambodia, where we weren't "officially" supposed to be.
The M170 probably made a good flightline vehicle, the extra bed size was perhaps good for carrying more gear and ammo out to the waiting vehicles than, say, and standard M38A1. See the peacock painted on the driver's side just forward of the footwell? Is that unit specific, or just someone's idea for a good piece of artwork?
