On the non-body color firewalls, where are the paint-breaks, that transition the firewall color from the main body color. From an efficiency standpoint, during assembly, it makes sense, that the interior color stopped at the jambs, windshield lip & back glass lip. Although not impossible, it would be highly unlikely that the interior color wrapped around the "A" pillar and across the firewall, since there would be a great deal of masking required, to transition the interior color at the firewall, to the adjacent surfaces, which then become the main body color.
In my travels, I have never seen an unmolested cab, that has the interior color transitioned across the firewall. Perhaps it was done on the early trucks, say '60-'61...
If I read something from the Trucks Sales Data Book or The Silver Book, I usually take it literally. Especially, since most of the literature is original and published before I was born. Learn something new, every day.
