Hello Howard,
I don't know if you have acces to Wheels&Tracks number 31 of the late Bart vanderveen, but on page 39 (in the article about GMC CCW-353) you will find two pictures of such a truck in the colours of the Australian army during the war and one pre-war picture of a Dutch example taken in 1947 in Netherlands East Indies.
The Australian ones are coupled to a 7-tons GS semi-trailer. These trailers were originaly coupled to Dodge T110L5 Ford V8 4x2 and 'Blitz' 4x4 tractor units. The conversion was done by General Motors-Holden. Maybe some Australian collectors will have photos of these combinations. Maybe you also can try
http://www.mapleleafup.org.
I've got also a article of field modifications which has a photo of a American used GMC modified to tractor unit during ww2, the trailer was build with parts of another GMC.
Give me a PM if you're interested, then I can sent a scan to you of the article of field modifications.
Greetings
Paul