AD_Pickup makes a good point. Although the parts catalogs say their step plates are exact copies of "original GM accessories" (I'm quoting an older Chevy Duty catalog), I also have an undated booklet "Advance-Design Accessories for Advance-Design Trucks" that doesn't mention step plates at all. Based on the illustrations in the booklet, I'm guessing it's circa 1948 or 1949.
I'm going to use 6cylindersovertexas's dusty footprints method of siting the step plates.
