I have used the plastic ones that have a large head that I have trimmed to fit a particular pc. They have several ribs and are about 1" long (I've seen longer) and come to a point. Easy enough to get into the holes of a 65 GT. I pick them up at swap meets like Moparfest etc. They seem to be pretty common though at most meets I have lurked. Just look for the vendors that have clips and things Like I mean lots of them and try some different ones.
