Glass , bumper , sheet metal all look well above average for 70 years. From what I can see of the box there was not a lot of heavy hauling , otherwise the top rail would not be so straight. If I found that one 30 miles down the road I would certainly be intrigued. UP Michigan roads were probably pretty salt free for most of the life of that truck.
See if you can communicate directly with the owner. At the very least his story may be worth sharing here.
