I think there are left and right ammo cassettes in the bustle. Since the gun is fixed in elevation in the upper half of the turret, it is fairly straightforward to have the autoloader feed a round into the breech. The spent casing is automatically ejected out of the turret rear via a small hatch. When the cassettes are expended, the crew must go outside to reload. I believe that the two cassettes can be loaded with different ammo, say AP and HE, so the gunner can select the appropriate round.
I wonder what kind of ride the commander and gunner had sitting in that crazy oscillating turret? The AMX-13 was an interesting answer to get an autoloading main gun into a tank.
I built the Heller kit back in 1980, and that was the first time I had ever seen this unusual design.