Like 3B said, you are looking at factory Power Divider shift levers (first introduced in Chevrolet trucks in 1956). The 3-speed Power Divider unit has one input shaft from the main transmission and two output shafts (one to each rear axle). The front axle is always engaged and the rear axle free wheels when rolling along on hard roads or engaged when off road or in a hard pull. The Power Divider has three gears, 2.22 under, 1.22 under and 1:1 Direct. It will more than likely have a Clark or Spicer 5-speed main transmission.
Finding a Chevrolet TF truck with factory tandems is a rare thing!
Mike B
