Anyone have any idea what this part is called and if it can be installed/replaced? (picture attached). It is missing on my driver side window, so I think that is why it is missing the upper stop and going too high. Thanks.

 

IIRC, some are pop riveted in, and some have a spanner style nut. It can be replaced either way, but the glass will need to be pulled. Because the nut style has locktite on it, and it is on the door skin side of the window. You may be better off just replacing the glass at that point. Hit the boneyards.
Note, there are at least two styles of this part I know of, not interchangeable, they are set at different heights and can't be adjusted to compensate. Yours look like the ones on my 86. The other style I know of has a hole that receives a "hook" when at the top of window travel. Had them on an 89 replacement door and caused me issues when I went to put my old glass in it.

 

Heres a part diagram and pics.

I have had no luck finding the window stops either new or used.
Used are usually broken anyhoo.......................

 

Its called a "stop"