Chevrolet 1533X2 30-cwt trucks

[cletrac (RIP)]

Here's the caption off this one with full windshields from IWM.
Members of the Long Range Desert Group (LRDG) inspect newly-issued Chevrolet 30cwt trucks in Cairo, May 1942.
The firewall area on these trucks can't be made flat since the old stovebolt has to stick back there somewhere.
The flat cowl bit is where the shape in line with the cowl vent is carried through to the dash with no windshield frame. The type of windshield wouldn't matter since they usually threw them away anyway. A windshield would have got in the way of the field of fire on some of their MG mounts and a reflection from the glass would acquire unwanted attention from many miles away.
I don't know if you checked out the New Zealand WW2 site but they have quite a bit in the LRDG. Here's the link.
http://www.nzetc.org/tm/scholarly/name-011342.html