Maybe I'm misreading it but looks like the first numbers of the serial number are DF869. If I'm reading it right, that would be the series truck. My book lists a DF861, 862 and 863. Am I reading the tag wrong? It is a little fuzzy in th photo. The handle on the steering column would be the trolley valve. It is for extra air to your trailer brakes. It may have "not for parking" engraved in it. The knob on the gear shift would be your 2 speed Eaton axle selector switch. Pulled out is high range, pushed in is low range. It is probably what we call a drag axle. That is the Eaton 2 speed is the drive axle and the axle behind it is a dead axle like a trailer axle. I think the DF was the largest series GMC made in those years.
