Hello Tom,
I wrote the "1940 Interior Painting" post a short while back, so my info is related to my 1945 1/2 Ton. My experience is, the cab was painted as a unit. The previous owner had painted mine with a black undoercoat, so I can't speak directly. My educated guess is, the underside of the cab would be Brewstwer Green.
The back side of my firewall, I'm pretty sure was orignally painted the same color as the floorboard components, which is Turret Gray. Maybe you have a piece of floorboad with a matchable section of paint. If you read my post and would like the formula mixed to match my '45 color, PM me & I will give it to you as well as pix of my floor/firewall.
Idaho Jake
