Emissions Control System ID help, 1971 Duster 340

So if ECS was on all A-bodies by 1971, and typically the fuel cap options are either “w/ECS” or “w/o ECS”, I’m seeing just one option I can choose. That would be “w/ECS” and that would make it a ”non-vented” cap, correct?
Pretty certain "yes" that is no vent on non-ECS