I don't care for the original retainer metal clips used to hold the rear upper stainless molding on the quarter panels. The ones on the doors are plastic and work well. I was thinking about the old school metal retainers that had a nut on the inside. Was not sure with the quarter glass removed if I would have access to the nuts from the inside of the car (72 GS hard top).
You can buy snap-in clips and not worry about nuts on the inside. I did this with my 70 Skylark that I added the moldings to. It's a larger hole, but the trim covers it.
Found a retailer that looks to work, it holds the molding to the car with a nut. The only down side is the mounting holes would need to be off set by 7/64" depending on what direction they are installed. It would be Auveco part number 2744 or 2818, both are the same and one of the two have been discontinued.
Looking more into this see GM drill large hole because of the spring type retainer and the Auveco retainer has a very small stud (#10 x 24) , less then 1/4" or 5/16" hole GM had in there quarter panels for the molding retainers. Anyone know the hole size GM had on the 70-72 for the upper peak molding installation?