They have a stud that goes through the fender & quarter, than a nut behind the fender gets tightened down and that holds the ends in place. Unfortunately, they are not reproduced for 1973, not even Glazier Nolan has them.
You could try talking to Mustangs Unlimited. It shows that they have them in the rocker molding kit. But that means you have to buy each side rocker molding to get them. How tall (inches) is the rocker molding? That or try contacting a place that junks Mustangs. I know CJ Pony Parts has a "bone yard" and I think Missouri Mustang does too. They might have a junked car that they can pull them off.
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