I suspect you are correct on the 2 screw holes I circled.
Also I said 2 screws for the lower support and I only see one.
Regardless, using your picture of the vent window assembly, I can see 5 tabs mounts for screws.
The poster should be able to look for corresponding holes in the door.
If none, then the doors are 1950 and older.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."