70-71 Duster rear side marker light resto

I would like to make these super nice, obviously the exterior gets painted body color but im interested in the area that you see in the trunk.
Mine are kinda crusty and would like them to look factory correct. To me the steel retainer looks to be zinc plated, what about the body of the light ?
Mine is a chalky grayish color, im not sure if its the factory coating of some kind? was the body zinc plated also? what is the body of the marker light made of?
any help would be appreciated, im shooting for factory correctness...Rich