So if I understand you correctly, the machine is effectively full-time free vend, it's just not obvious?
You would have to have a solenoid at the bottom of the stack to push open the lower stack parts to free the lift gates.
Commonly found in the Vendo 81 when they removed the vending cam and added a solenoid. This allowed for higher prices, and electrical coin mechanism.
So, the current set up would need to have the lower stack parts would have to be removed on the can stack, to make free play. The original mechanical coin mechanism is there for display. But you could put a coin in, crank the handle and the coin would drop in the box. The linkage arm in the inside would move but since the vending cam would not be present. Normally when the crank handle is pushed down it would move the linkage arm and turn the vending cam from the inside to free the lift gates.
Jared