My car, 8MA670, has open vents and an aluminum panel on the inside of that encloses the three vents. It is sealed off with a nice aluminum panel that is about 30 mm deep. It has an attached tube and hose for water drainage.
As a car designer I can give you a pretty good guess about the vents and their functionality. This could be a likely scenario.
THIS IS MY ASSESSMENT OF THE CONDITION BASED ON EXPERIENCE:
Originally Giugiaro probably thought of them as intakes for the carburetion. His design work shows a strong and consistent effort to link functionality with aesthetics.
Notice that the hoses that were used to bring cool air to the carburetor were taken to the back of the car, away from the headers and outside of the engine compartment.
As the design developed and the mechanism to allow accessibility to the engine compartment was finalized it became apparent that this idea was not workable. Take a look yourself, flexible hoses or hard box shapes to link the engine covers, when they open, to the air cleaner would be very difficult and cumbersome to create and be robust enough for years of use.
The gas tank would also interfere with this concept.
In the meantime the design was becoming finalized and I am sure it was very well liked, so the vents became more of an important aesthetic element than a functional one.
If you made a link from the aircleaner to the vents that traveled through the two panels that arrive on top of the engine when the covers are closed you would have a very difficult sealing situation.
Also, the vents collectively are too small to supply enough air under full throttle.
It is also very unlikely that the vents collect air as they are depressed from the normal surface with no aerodynamic device to draw the air in. A small vertical blade 10 mm or so, traveling vertically along and in front of, or behind each vent might do this, still air volume would be very low.
The vents are however at the top of the car and could possibly serve very well as hot air exhaust, like a smokestack. You still have the water problem, if they are open without the water-catcher behind them.
You could open them, make a water catcher like the one that I have, but allow it to be open at the top. This would allow hot air to curl through the top opening and out the vents.
I don't think it would be worth the effort.
My car runs cool now, all sealed up with the engine covers in place. Since I did all my cooling modifications my engine has not seen 190 degrees, even in some 92 degree weather. Underhood temperatures on cars today are far higher than what was considered hot in the Mangustas time. If you use modern water hoses for radiator and heater then the only other element to worry about are the wires. New ignition wires can withstand very high temperatures. A little foil heatshielding here and there for items close to the headers works well for very hot places. For the engine, Mobile-1 is my choice for internal temperature reduction.
In the end, forget it.
The Mangusta has a lot of cooling space around the engine. Behind it the compartment is open where negative air pressure draws the air out when the car is running and allows it to escape naturally when the car is sitting.
Compare it to a C-6 Corvette that runs fine at 220 degrees on an 80 degree day, in traffic, with the engine tightly enclosed on all four sides. The modern materials allow this to happen.