What is the diameter of the fresh air cowl vent opening?

When I rebuilt the heater and driver's side air boxes, I noticed some rust and holes around the openings to the air cowling. Had my *** on fire to get the car road worthy for the trip down the coast. Now I'm thinking about what I didn't think about in the early fall. Anyone have the inside diameter opening for 64 Dart?

Thanks in advance and Happy Holidays!!:thankyou: