Noel Anderson

I am having a hard time installing my 1969 Cutlass Supreme Holliday Sedan rear wheel arch trim moulding, and can not find anything about it in the Chassis Service Manual or Assembly Manual. The car body has seven holes for clips in order to hold the moulding on. The last four holes are through holes and I can use the standard Au-Ve-Co 12958 or 12960 clip and nut on. The fist three holes are a different story. They are slightly bigger than 5/16" diameter but smaller than 3/8" and there is no way to access the back side of the hole in order to screw on a nut. I have been trying to use these push in clips with foam https://www.ebay.com/itm/192446915851, but they will not stay locked in place so the moulding pops back out. Am I using the right clip? Is there a trick for installing the Supreme style of wheel trim? Should I drill the hole to 3/8" and use a bigger clip?

Thanks,
Noel