I think he's talking about the c-channel that goes around the door window glass.
As far as I know, these were only available painted steel. The inner and outer trim pieces that actually attach to the door were stainless if the truck was a deluxe model, but painted otherwise AFAIK
You might try contacting Joe at Mother Truckers in Tucson and ask him. He's forgotten more than I know about AD trucks. He posts in the Classic Parts Talk website once in a while under 'Deadzonetruckin' and in the Facebook Chevy 3100 group. The last contact info I had for him was
mothertruckeraz@aol.com