To answer my own question: the trim clips are put in first. They are nylon clips with a leg the fits through the hole and a post that spreads the leg out on the opposite side of the metal to hold the clip in. The trim piece snaps over the clips. My undersrtanding is that the clips are no longer available.

I'm in the process of installing power steering so if anyone has any helpful hints, lt me know. I'll write up a source of parts and take pics as I go to post later.