66 Belvedere I side view mirrors

[66four40]

My car has a single posts side view mirror, but I have seen them with a dual post. Which is the correct one for a 66 Belvedere I. I searched the web for answers but was full of pictures of cars with both. There is a dual post for sale very local to me and was wondering if I should pick it up as I am trying to remain stock looking and period correct.

Thanks,

Derek