I was fortunate enough to get a copy of the Sept 1942 article when Army Motors was talking about the 'new' wooden cargo beds for G506, G508 and other trucks.
We all know this was to conserve steel, but there are other tidbits:
The wooden beds were scheduled to be installed on new trucks starting On September 1st 1942.
There are over 700 fasteners used on the 353 wooden cargo bed.
There were 11 different wooden bed sizes (from the article).