[Bluejay]

There was a kit developed for 65-66 Mustangs. I would bet your Falcon would be the same. You are correct about the Vent openings rusting out around the trurned up edge. What you do is go up from underneath, thru the opening and clean the rust as good as possible. I used sand paper, a cordless drill, and a dremel. There is a plastic "tophat" that fits over the vent. You use a fiberglass kit to "glue" the top hat in place. Then I covered that with an insulator, roofing patch or tar. It is a painful chore as you are standing on your head and you have to reach up in a tight area and can't see what you are working on. I had to remove the seats to have enough room to lie in the floor. Hope this helps.