This is interesting. Why did people along the way change mirrors from the originals? Were they two-screw stolen? Were they knocked off in an attempt to race thru a car wash stall at 2:30 am after a few slo gin fizzies in high school?
Hard to beat the originals and they are dirt cheap these days. the screw bosses are under the door skin for the passenger side so my leanings say, buy a set of used originals, mount them and drive safe and happy.
Sidebar: When the vandal dirt bags in Socal smashed my C4S passenger side mirror and mirror body at a ball game in SF, the 1K deductible didn't get one quarter of the way there to replace it. I really like how cheap 914 stuff really is.