Found my dads original 1971 duster!

Bennoel 10 said
I believe that from the factory it would have had slots in the parcel shelf. (the board covering the rear shelf). I'll try and get you a picture of a 69 dart as reference.

Here’s mine. It has slots for speaker holes, but nothing for the rear vent. Forgot. Headliner is all fixed now! My friend who does upholstery has it looking mint