If you check out Bratton's Antique Auto Parts,
www.brattons.com
look under 'pick up cab parts'. Specifically, they list their part #32180
which is called the 'Pick Up Door Panel Nail'. It consists of a plastic insert that goes into the holes around the inside perimeter of the door, included is a large headed pebble grain finish 'nail' that goes through the trim panel, and into the plastic insert. Their catalog shows an insert and nail for $1.50 each, 24 needed per door. This'nail' has rings on the shank that hold into the plastic. I believe the originals were a similar affair, but all metal.
The trim pieces up the lock pillar and across the cab at the top of the door would have similar looking 'nails' but were actual nails.
I'm sure other vendors offer these as well, just happened to have my Brattons catalog handy.
Best Regards,
Stew Masche
Lake Mills, WI