[1960HDGMC]

Nice project Steve. The Forest Service tie in would explain the green variation from standard vinyl choices. One line to research would be the states and USFS archives from this era. There are archives in each state and regional US Archives (southeast archives are in Morrow, Atlanta). You can search online and visit them to research GMC and vehicle records. Plenty of untapped pictures and info exists, just in need of finding. Any production numbers info you can find may or may not include fleet vehicles such as this cool truck. If you can find out the USFS vehicle numbers, you will have some idea of the overall number built for the year. I would imagine that USFS and power companies attest for a big swath of these particular vehicles. Good luck with the project, GM