I did this modification to my Barracuda as well, and yes ¼ inch holes are correct, but as suggested test the clips to the hole prior to drilling all of them. Mine where lose in the ¼- hole and does not hold the trim tight against the body panel. There are four clips that actual have a nut on the back of them no one could tell me which holes or trim pieces they corresponded to, so I use one on each trim piece, top, bottom, and to ends.