[Grant Bowker]

The 16" wheels suggest 30cwt, particularly with cab 11.

I think of the C30 as 134" WB only, might be wrong on this. The space between fuel tank and rear tire looks more like 158" WB than 134" but I can't clearly see the intermediate driveshaft suppor (2 piece shaft) of the 158" WB.
The body resembles a 3E1 Office as show in Clive's "Drive To Victory" for proportion, placement of door, windows, accesses in door and body side, presence of luggage rack at rear of body (which shouldn't be present on a 3G1 ambulance body as it would block the rear doors and the 3G1 shouldn't have the side door) but it lacks under body storage boxes shown in the book. The presence of the tire carrier is similar to that described for a 3G1 when mounted on 158" WB. There also appears to a wireless mast at the front left corner of the body. If the truck had a wireless set, I would expect to see provision for a chorehorse either in the body (either as found at the right rear corner on HUW and C15A with 2K1 body or in a box on the chassis, I'm not sure where they were mounted on longer wheelbase wireless trucks). Clive had photos of what looks to be a similar body on a cab 11 134"? with 16" wheels F30? WB on page 107 to illustrate Lindsay body construction.
The presence of the speaking tube between cab and body fits with wireless trucks but could apply to any vehicle where crew members rode in back while in transit.

There was a 158" C60L with 16" wheels made for ambulance use but I would expect a longer body on that, without the luggage rack and with rear rather than side door(s). The C60L with 16" wheels and light front axle was also sometimes found on "Australian contract" trucks in Canada which I believe were usually cab 13 produced too late for shipment before end of war.

I wonder whether it is possible that someone mounted a 3E1 body to a C60L chassis, removed the storage boxes and added the wireless mast to fulfil a need?