Can't help with the rumble seat but the only thing plated on the door hardware is the dovetail. Everything else is body color except for the spring loaded pieces the dovetail fits between. Those were/are black on my car, which turns out to be body color on my car but they were/are not painted.
VCCA Member 43216 Save a life, adopt a senior shelter pet. 1938 HB Business Coupe 1953 210 Sedan
The sorta rounded cover over the latch should be body colored in your original red car photo. Dovetail and the stepped wedge should be raw/naked as they appear in the photo. Not sure about the rumble.
1938 Canadian Pontiac Business Coupe (aka a 1938 Chevy Coupe with Pontiac shaped front sheet metal - almost all Chevy!) 1975 4-speed L82 Vette