Mike,
I have been patching holes, tears and damage on my 1942 g506 donor cab (ca~1942) and have measured the following:
Toe board, floorboard, engine lower side panels, outer cab skin, interior back panels, door skin and interior trim parts are 20 ga.
Engine side panels, dash, interior door panels, and firewall are 18 ga.
Cab bottom and front fenders 16 ga.
Why Chevy chose the thinnest gage for the toe and floor board is a mystery. The beds may be different gages due to the duration of the war effort. My 41 bed is 10 ga where later 1942 are 14 or 16 ga.
I am not an "expert" fabricator or body man, but I have been patching panels by matching metal thickness. At lunch time at least once a week, I cruse the scrap metal yard in search of post industrial production remnants. I have found that 20 ga is not very common, but does show up once in a while. At least in my location, 18 and 16 ga is plentiful (depends on the factories in your area). 10 ga is tough, but I happened to come across a piece complete with a needed 90 degree bend last week. My scrap yard charges 20 cents a pound for steel, so I typically walk out with about $5 worth of patch/fabrication material. It is kind of addictive, like a women collecting shoes.
Hope this helps.
Paul
