The after market square clips will keep them from turning just like the originals. The original clips with the wings tension the clip so that it does not move up and down the trim.
I have bought the fender trim clips available at Dennis-Carpenter which I think are made by Mac's for the fender stainless trim. They are just square with a screw attached. All of the normal sources I know about show the same type. The part number for the original clips in my old Ford Chassis...
I am working on a 1947 Super Deluxe Coupe. I see that rear footrests were installed in some of the 47's that I have seen. I do not think I have seen them in a coupe only the 2 and 4 door sedans. Were these standard on certain models or available as options etc.