I'm trying to bring my 67 RS with an original 327/210 back to as close to stock as possible. Found the correct dated 2 barrel manifold and original air cleaner, and have a line on a rebuilt Rochester dual jet, but can't seem to find out anywhere why some cars were set up with a positive system (vented oil fill cap/breather) and others a closed positive, with the pcv valve attached to the fill tube.
Do you have an Assembly Manual? The standard (non-California) crankcase vent system is shown in UPC 6, sheet C5 (adapter elbow, hose, PCV valve, and carb fitting, with vented oil fill cap), and the optional (mandatory in California) RPO K24 system is shown in section K24, sheet A2. You want the standard setup.