On a 1975. What are all the correct clips and screws for the rear valance that has the fender flairs?

Is there a clip that helps hold the end of the valance, where it sits directly behind the back side of the tire?

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No & No. The correct clip for the valances are short & wide & rather uncommon that Ive found. At the ends they just use a some M5 hardware to attach sandwiching the spacer.