The way to tell the difference between a pictured tractor being a Stolper or Hinson is look at the cab top. The Stolper used a modified 2 post Roll-Gard canopy top and the side line tapers from front to rear. The Hinson used a formed fitting roof style top that wraps over the cab sides even from front to rear. The year break is from 1970 models to 1971 models. So 4520 tractors are all Stolper cabs, 4320 and 4620 are all Hinson cabs. 3020, 4020 and 5020 can be either, depending on model year. There were never any rear entry cabs using the internal 2 post RG structure.