This is the first time I have ever seen a closed cab with a wood bed that can be credited as to source. I've found other photos, but none were sourced.
Detroit, Michigan. Army truck hauling boxed freight
http://www.loc.gov/pictures/collection/ ... 023034/PP/
Production wise the wood bed started in Sept 1942. The closed cab ended in early 43 (March, IIRC) so that's only a 6 month window for the possibility of a factory closed cab with a wood bed. Of course this could simply be a replacement bed for a damaged steel one.
If you look at the registration number 4134998 would put it at a late 42 production timeframe... steel beds would still be in supply.
Very, very interesting photo.
I wish I could make out what was in the crates.