GC-Convert,
Glad to be of help! And it is great to see another Gran Coupe being restored as a Gran Coupe!!
I bought the clips at the Don Garlits Mopar Show from a vendor of generic clips. unfortunatly i don't recall the part number, he just had a bin full, and i figured what the heck, give'em a try!
I noticed that the length of the "post" on the clip was just a bit short of allowing it to 'pop' into the hole in the rocker panel. There are indentations at every 1/8" inch or so at each end of the clip, and after having clipped off the ends (they are about 3" long) to fit inside the molding (They need to be just under 2 1/2" in length), i used the end pieces that i clipped off, and stuffed one in between the clip, and the molding. It pushed the "post" out enough to 'pop' into the hole.
I didn't try other clips from other years, but it is possible that there might be an alternative. The width of the post in the generic clip just happened to be the right size, so i guess i got lucky in that regard.
As far as another method, i do not know of any. Finding a analternate clip is probably the best idea. I tried to make my own, using stiff plastic like a credit card, and black nylon round retaining posts thtt i bought at Lowes, but found the generic clips just seemed to work better.
Maybe someone else can chime in.