intake gasket ?

It's not as much of a "vent" as just open space to let the iron around the crossover port expand from the heat and not cause cracks.

Unless you plan on driving in sub-40-degree weather a lot you don't need the exhaust crossover open especially with an aluminum intake manifold (aluminum transfers heat from the engine up to the plenum/carb area much quicker than iron). With today's crappy ethanol gas it'll just cause headaches from overheating the carb and boiling the fuel all the time.