Somewhere around '63, or '64, PCV (positive crankcase ventilation) became standard on virtually all OEM's. Prior to that, engines had road draft tubes to vent
oil vapors.
The PCV pulls a vacuum on the crankcase through one valve cover, and fresh air in through a breather the other valve cover. It allows
oil vapors to burn, rather than collect inside the engine. Keeps the inside of the engine cleaner.
You can run the engine without it by using another method to vent the crankcase vapors. If the Weber setup has no common plenum or vacuum source, you'll have to find something else.