Dave;
I came across this while I was looking for something else, don't know if it will help or not.
From a pub I have entitled
British World War Two Military Transport, Light Utilities, Lorries, Heavy General Service Trucks:
"The K5 and the Bedford QL chassis were selected to form the basis of a portee vehicle to carry the 6-pounder Anti-Tank gun, and Canadian Military Pattern 3-tonners were also used for this purpose. In this form the cab tops were removed and replaced with lower canvas soft tops to enable the gun to fire forward over the cab whilst still in the vehicle. When the requirements for this type of vehicle ceased after the end of hostilities in North Africa, all these portees were converted back to General Service configuration. Standard wooden or metal GS bodies were fitted, but the soft top cabs were retained."
Attached picture is of an Austin K5 ex- Gun Portee converted to GS configuration, with soft-top cab.
Cheers