They were playing around with the emission systems these years. I think 73 was the only year they installed the osac valve in that location and later moved it to the air cleaner.
Here is a pic of a 73 Swinger with the holes and a 74 without the holes.
Being from Maryland you probably aren't aware California cars of the early 70's have lots of crap 49 state cars don't.... 72 got an Osac valve that was slightly different from a 73 Osac valve...
We got unique fuel filler necks that took special gas caps... We got EGR valves before anyone else.. We got cars that couldn't have exhaust tips when 49 state cars had them... California has had mental giants in positions of authority for waaaaay to long
