None of those ebay mirrors are correct, the base is wrong. However, the wrong base is also what's used on ALL non-original Cobras, so one of those vintage ebay mirrors would probably bolt right on. Even on my own car, installing the correct mirror was a challenge because the bolt spacing is different.
The proper Lucas mirror (as seen in Bob's pic above and mine below) has a longer stem, a non stepped base, and the base is hollow underneath and has a rounded top shape. Also, the "clamps" that hold the glass on an original mirror are not symmetrical, there is one long and one short so the stem is actually offset on the glass.
And depending on how technical you want to get, most S/Cs had the mirror stem pointed forward, not back, and the mirror is supposed to be about an inch to the right of center, not centered on the dash (I won't be changing that anytime soon).
Here's a pic of my original mirror in my car. Look carefully and you can see the end of the "clamps" behind the mirror and see how they are not in the middle of the glass....
