check for a second strap location on the inside surface of the drivers side shock tower - low
added some more pics that does show a hole in the area that you mentioned
Think if you do a search we discussed these straps a while back. Or it could have been another forum
found a topic or two that discusses these straps, with suggestions on making ones out of a 3/4" wide fan belt
You mentioned a plastic retainer - When and where was your car built? At San Jose I've seen metal retainers similar to some of the firewall pad retainers
per footer Dec 66 SJ. the one retainer that survived is plastic, and the other forum topic talked about a "plastic rivet". Mine is more of a push pin device and would have to dig out of a box to get a picture. Definitely not the same fastener as the long metal christmas tree type on my firewall pad, but then again I don't know if the plastic is correct.
Thanks Jeff.