I am starting to tear apart the mustang for restoration, and am having a difficult time with the lower valence retaining clips. They look like there there to align the valence with the body as they are also attached to the front fenders. Everytime I turn them they just lift that particular body part up or down. Is it that they are just old or is there a trick to them?

 

I don't recall having mounting clips on my valance. They just bolt on using bolts and nut clips. sounds like your nut clip is turning.

 

Same here. Only my chrome trim uses the clips.

 

The clip are probably corroded. Be careful removing them that you don't bend the sheet metal.
I had to use a liberal amount of WD-40 and vice grips to hold the clips so as to avoid bending the metal.
I had to hack saw one off.