Isn't the rear view mirror on a '69 supposed to attach to the roof?

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OK, not to hijack the thread- but can someone tell me if they have drilled the three holes to mount the factory bracket? And if so, what size drill bit? My truck came with no mirror or factory holes. I picked up a bracket and mirror today at the junkyard that I would like to install. (actually, the mirror was crap but I found a mirror in a 70 impala that worked- I just love scrounging around the junkyard!)