These mirrors were a factory option on the Art Deco series, but I believe only on the 1 1/2 and 2 ton trucks, and only on the driver's side doors. The mirror was a long rod straight out from the front hole, with a support brace connecting from the rear hole, and a small, round drop-down mirror. They were useful for seeing around the sides of large stake beds, ie: farm trucks.
The mirrors are very rare, and not currently reproduced.
At least, that's what I think.
-Michael