Here are a few both GMC and Chevrolet. All are NOS (except mine). I paint my own and you can putty and finish them just like new (they are double thick and don't respond well to hammering). I use white refrigerator enamel and as strange as it may sound mask a couple letters at a time. Spray them with enamel, remove the tape within a couple minutes and using bamboo skewers from world market and Q-tips, carefully scrape and remove the overspray. Time consuming, yes.
https://www.flickr.com/photos/advance-design_parts_co/8129054429/in/album-72157631867396207/
I also restore Coke machines and use the same technique on the white lettering.
https://www.flickr.com/photos/advance-design_parts_co/27235446102/in/album-72157631866985745/
With practice they look fantastic and the enamel holds up well.
https://www.flickr.com/photos/advance-design_parts_co/16292779369/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/18994720244/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/22029109475/in/album-72157631868452754/

1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr