The Stolper cab, built around the 2 post Roll-Gard and using a modified RG canopy, was the first factory AC tractor. I think it was offered on both the 5020 and 4020 Diesel tractors about the same time, either 67 or 68. Not ever offered for 3020 or any gasoline 4020’s. 4020’s got a 24V Motorola alternator and different radiator cooling parts, water pump, pulleys, belts, damper and etc. AC compressor under the hood and condenser mounted under the rear of the canopy top with electric fans. This design was used through 1970, similar design for the Hinson cab then in 1971 and 1972. 4020 compressor moved to the lower left hand side block location I think for 1972 models.