The eBay listing does appear to be the correct part you need.
There is a spot on dash already pre-drilled (with a “D” shaped hole) on ALL F and M-body cars, for Right side mirror knob.
What is not pre-drilled is the two holes on front side of door or body side of door jamb – as well as holes on outer door skin.
If you remove the driver’s side (Left Front) door panel, you will see three holes pre-stamped on inner door frame – for the three mirror nuts.
The same three holes will be on the inner door frame – once you know where to look. These holes have to line up with mirror studs
or you will have a hard time attaching the mirror.
My recommendation is to unscrew the Left outer mirror from door – but not remove completely. With the help of a friend (to prevent paint damage), make a paper outline/template from front of door and top of door with all of the different holes (you might have to cut out a slot in template for the cables). Also record the different size hole diameters.
They use one (or two - I can't remember) plastic clips to help hold the inner mirror reinforcement in place with. These small clips are optional.
With that template – go to other side door and mark it for drilling.
With one of the nuts from Left side – use it to find three nuts for the Right side.
The next hard item is to find the plastic gasket and metal support bracket that goes inside of the door (reinforcement – which is important to have in place).
There is a knockout on R/F door for mirror cable (black arrow), so a person can drill or take a hammer and punch can knock that small piece of metal out. A person could also use a holesaw slightly smaller size and drill it out. After drilled or knocked out, take a file and smooth out any sharp edges. It might be easier to do with R/F tire removed and fender shield removed.
The cabin side of door jamb may have two or three knockouts on it. One is for radio antenna (if equipped). One is for electrical wiring harness (the big hole). I need a mirror to see the third hole on my car but it should be there (so no photograph of it). If you can't find it, you can make a hole of the same diameter of the mirror grommet on the jamb somewhere - just make sure there is nothing behind it to cause an issue.
In my case - with no power windows or door locks, I would use the wiring hole and make a smaller hole on it (red arrows).
Lastly, there is a hole that needs to be made to the panel under the steering column, with a plastic trim ring to be added. The hole is already marked on back side of the panel for location – but it is easy enough to find a panel with hole (and trim ring) already in place, and in a matching color.
I did forget to take pictures of these parts - but will later tonight.
Note, my '77 wagon did not come with a Right side mirror, as well. I have a NOS mirror to install - so I will be performing the same procedures, when the time comes.
BudW