The positive crankcase ventilation (PCV) system vents harmful blow-by fumes from the engine crankcase into the engine air intake for burning with the fuel and air mixture. The PCV valve limits crankcase blow-by gas to the fresh air intake to suit the engine demand and serves to
prevent combustion from backfiring into the crankcase. Thus, the benefits from the PCV system include the ability to:
Maximize the oil cleanliness by venting moisture and corrosion from the crankcase.
Protect against excessive crankcase pressure.
Automatically regulate the ventilation system air flow to the engine air intake as required by engine operating conditions.
Follow the PCV hose from the throttle body to the intake maniforld under the plennum from the driver's (left) side. IIR the PCV became required by law at about 1962 (63 model years) as part of the solution to pollution from automobile emmissions. Prior to the PCV the piston "blow-by" into the crankcase was vented via a crancase vent tube directly into the atmosphere. Also keep in mind that gasoline had a lot of lead in it back then.
Added thoughts; some model/model years have the PCV valve in the valve cover.