Well... it's a primitive date back (very early model) mounted on a bulk loader adapter and motor drive... that way, you can shoot either 250 or 750 frames without stopping to reload... all depending on the model...
The type of monster I really wish I had created...
Here's a picture with the back open that I found in a Nikon Handbook...
[Sorry, image deleted during forum software upgrade. Please re-upload if so inclined.]