This one was made into an auxilairy, by cutting the transmission's main shaft, and having a slip yoke welded to the low/reverse shift collar. A roll pin, and a set screw keep it together.
The tailshaft housing varies depending on who was using the unit, but the guts are probably the same. Most of the Chevy's I've seen are similar to a modern transmission, with the slip yoke and seal on the rear end. I think this one is a Nash, Kaiser, or Rambler unit, but not sure.
Mine is lacking the governor, and speedo adapter, that yours probably has.
I have a 65 Chevy pickup unit at the shop, now, that on a SM318 3 speed.