From scanning through my Dad’s books, it is a ‘Swiss entrance’ used to control ventilation. I would also imagine that it is used for prevention of access to the hive by lizards, field mice and other small creatures. They are available on Italian bee keeping sites.
Looks like a mouseguard to me. How much difference in ventilation would there be moving the plates apart? Absolutely none if you have a mesh floor and little with a solid floor. Definitely a mouse guard
Mind you it’s 1956 so would be a solid floor