What are these???

Correct about the osac valve - the round one was for another emissions device that was used on California models - an addition to the osac valve if I remember correctly. What I did on my 73 was make a nice plate to cover up the osac spot out of Aluminum, painted it and the round cover and put them on using the original style bolts. Looks decent and nobody really cares if you dumped the osac valve anyway.