About 20 years later, the "mirror on the front fenders" craze hit Japan - if you look at pictures of cars sold in Japan in the 70s and early 80s, you'll see the same odd placement.
============The Japanese government had a rule that mirrors be visible from the swept area of the front windsheild, hence the appearance of mirrors out at the end of the fender at that time.
Similar thinking could also be part of the logic behind placement farther up the fender on Imps, but I'm just speculating. The curved glass could make them useless as stated earlier, so be careful The closer the mirror is to you, the wider the field of vision, so I'd root for a placement on the door for practical purposes.
-Kenyon