Thanks guys, great info!
Now, I really thought I’d got it sussed. The pics that Cletrac first posted proved to me that the 1533 Chev was an open cab truck. Then I got thrown a swerved ball/bowled a googlie (depending on whether you follow baseball or cricket!) by the photo of the LRDG truck, the one with the guy ‘firing’ the Vickers K.
If you look at the ‘door post’ near his holster there is a door striker catch. This part at least looks like a cut-down closed cab. I am totally confused now! The 1533’s used by the LRDG appear to have an open cab dash/windshield area (flat like an open cab) but a cut down closed cab rear. For my sanity can anyone offer any comment?