There are several different clips used originally (depending on what panel the molding is on). Basically, the corners/ends had a stud type plate that slid into the molding & a speednut went on from the back (the fenders & cab corners used only these). The other areas in between those (length of the bedsides & doors) had square plastic clips with Two sided tape. The tailgates used another clip on some years that was like a "V" & slid on the molding & pushed in a hole on the ends. It seems to me that some fenders had a Phillips screw at the back, next to the door.
The way I've set-up to drill new panels is this...Tape/have someone hold the moldings in place, draw around them on both sides with a pencil, then remove the moldings, split the width in half & that's your drill line. On the fenders, there are access holes in the inner panel...be sure to line up your holes accordingly. Lay it all out, drill, then paint. If your Two toning, the holes become your guide as to where to tape. Have Fun! Lorne