One more bit: I only have Chevy info, sorry. But it does give insight to GM thinking on plates and has to be included to beat the horse dead. All 1/2T info.
Source: GM Heritage Center/Vehicle Information Kits
1960 no mention
1961 RPO 399 "Special Serial Number Plate"
1962 STD equipment "GVW Plate 5000 Lbs"
1963 STD equipment "GVW Plate 5000 Lbs"
1964 Index lists Regular Production Equipment p 6, no p 6.
1964 RPO Z55 "Special Serial Number Plate"
1965 STD equipment "GVW Plate 5000 Lbs" and RPO (no number) "Serial Number Plate (State of Pennsylvania)"
1966 STD equipment "GVW Plate 5000 Lbs" and RPO Z55K "Serial Number Plate (State of Pennsylvania)"
