The basic vehicles are Morris trucks from Frontline Miniatures that were surplus as I added newer models to my 8th Army. it involved some careful sawing of the rear body to reduce it to a flat bed. The Bofors is the First to Fight model carefully assembled to fit in the available space.
A shelf was added at the rear of the flat bed and various stowage added. Crew was a significant problem and the only "gunners" I could find to fit were HaT British tank riders.