Hi Napco Man!
The info I have for 1939 GMC trucks, mechancical data, shows a 9600 model as a 2 1/2 ton. If it's a 9671-72-73 it would be 157" wheelbase. If it's a 9681-82-83 it would be 175 3/8" wheelbase. It shows it having a 224 cu. in. engine.
Hope that's helpful.
George