I believe the originals on a duster were the nylon ones.
I have seen the metal ones on earlier cars. The duster did use the metal ones on the plastic badge that goes on the inside of door panel.

http://www.ebay.com/itm/Mopar-Emblem-Trim-Retainers-62-Up-A-B-C-E-Body-10-Pack-13-/132317100720?hash=item1eceb6bab0:g:MEMAAOSwurZZLzIR&vxp=mtr