Jim,
Here's what I've come across on my 51. The entire seat assembly, except for the cushion frames is the "champaign" interior color. That includes the "skirts", frame, etc. Floor is interior color. E-brake pedal is interior color on the portion that protudes into the interior. Below the floorline it's exterior color. In other words, it was assembled to the cab, the interior was painted, then the exterior. The part that bolts to the pedal arm that the footpad slips onto was black. The rear cab wall was also interior color, but on mine the fuel tank was installed before spraying the interior. Therefor, behind the gas tank it was just primer. Same with the fuel tank, the side facing out was hit with color, the side facing the rear cab wall was unpainted. These trucks were assembled as much as possible at the factory before any color was sprayed.

Bob