Here are some stunning Post Office vehicle photos Larry found online--probably from the mid-1920s or so. Were they kits provided by the postal service, or were they home-made? Seems to me they were sharing the "how to", but added improvements as they occurred to the local builder/mechanic. None of the three pics are of the same vehicle, you can tell, but the second one is parked in front of the U S POST OFFICE PIERZ MINN. I bet the caterpillar-track six-wheeler was used for road-free areas, and skis were swapped out for the front tires after the first snowfall. I'm constantly in awe at peoples' innovative skills. Wow!
Larry said this last pic was in New England ☺