Father-Son 1974 Duster Project

What did the manifolds come off of, defiantly smog ones, with the holes below the ports.
They may need plugged on the back side, usually smog manifolds had a AIR set up on them.

They came off a 75 360 Roadrunner. I was more concerned that they had larger ports, but I never considered or noticed the air ports on the manifolds.

What methods can be used to close them up?