Take pictures of the mirror and the mounting area then search and find other cars built around the same time and plant. The idea is if they did it originally on your car it would not have been the only one (mirror base) delivered to the line (at least 200-500 units I would guess) so there would be others. Alone by its self its difficult to accept that it was factory especially considering the other changes pass owners have made to the car
If you can get three or more independent confirmations of the same thing you will have a much stronger case for giving the car and finding the "benefit of the doubt "
The mirror itself is long gone, which is why I started to work this out.
Because of the late build date, and soon to be started 68, I'm sure they had 10s of thousands of the bases.
Now I know that they didn't necessarily come down the line in sequence, but given the verified date, there are maybe a hundred odd more cars to go, and some of them could have been Cougars.
I think I could look for the rest of my life, (from Australia), to not find 1 more example, let alone enough for a pattern.
To prove something that is, (to me), obviously true.
I'm rethinking my idea that it will be easier to go stock versus modified,(I thought I would have a finish point).
Guess if it was easy, it wouldn't be fun.
Thanks for everyones input, it is appreciated.