These weights all seem to be ficticious to me. Back in the days when we had to buy regular truck plates we had to have a weight slip to get a license plate. Most of us would take off the spare tire all extra equip. sometimes the rear bumper,etc. just to get the weight below 4000 lbs.True the gross weight stated on your tag is a maximum reccomended loaded weight. But 3100 lbs for a half ton truck sounds pretty light.Most of the 1960s 1/2 ton trucks weighed in MT at around 3800 to 4100 lbs depending on how many extras were on it.I would think that the older ADs having heavier body panels would weigh about the same. Only way to find out for sure is to have it weighed.