Though I have no paperwork linking it to the Forest Service, your guess is looking to be right on. I am owner #7 of this truck. I have actually talked with at length, the 3 owners before me,(owners #4, 5 & 6) which go back as far as 1968 when the truck was in California. The #4 owner, now in Ohio brought the truck to Ohio when he moved there from Riverside Ca. in the early 70s, and said that it was thought to be a Forest Service truck, by the owner he had got it from...,(owner #3) which I have not found, but have a name and old registration card from that goes back to 1963. I am very lucky that almost everything really important to this truck like the numbered matching Marmon Herrington plate, dash shift tags , emblems, data plate, title etc., was kept together, and passed on from each former owner.