Carl-
Rick is right. That should be stainless. There were two kinds. One with a round mount and the other with the U shaped mount. The round seems to be found on early cars.. On your car I think either would be correct though. The round ones are hard to find. D&R makes a pretty nice 70 repop mirror with the U mount.. Hmm.. Did I look at yours at the reunion??
Original 10 inch 1970 only round style mount..
10 inch U shaped repop mirror from D&R.. Good mid 70 up to 73 I believe.
D