So after looking for my sales cat,
it does indeed reference both 3spd on the column as "Standard" and the AT column shift optional on the 1966 GTO.
Albeit not a popular choice, it was possible.
Andre,
It doesn't seem odd depending on her age when bought.
Most of the older gen grew up on MT/ST cars and likely a good number of them on the tree shifters.
If you ever happen upon this GTO again it would be great to document (pictures).
I'm am amazed that I could not come up with one example on-line.
I also recall a column shift GTO that was shown with a shifter block-off/Delete plate on the console with the owner indicating it was ordered that way?? I can't for the life of me fine the pics or the info; on year and such. Now that would be an odd one for sure.
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When I die, I want to go peacefully like my grandfather did, in his sleep.
Not screaming like the passengers in his car.