These are now some 32 years old at least as two of the roofs have 85 on them in rather good lasting permanent pen. The swivel allows the unit to be totally shut or open for mating flights. Some of then have an aluminium slide which I think he used to replace the plastic one supplied as they were rather fragile.
They have slots for 6 bars though normally only four were used and the food compartment (to the right) was not used for comb. There would be a thin plywood separator to keep the sugar to the right hand side.
The angle of the sides is 76 degrees to avoid the combs being attached.