My 67 had 70's style mirrors when i bought it. Much better visibilty but i wanted factory mirrors. I picked up a 67 remote for drivers side and the round 67 passenger mirror from a firebird only salvage yard. At the time i didn't know there was a difference, luckily the owner showed me the difference and didn't just hand one over that would work. The vent post doesn't obscure the mirror as long as you have a 67 mirror. Visibility isn't great but you get used to it. Now it looks as it should. If you don't have a 67 mirror i would think classic industries or year one can hook you up.
Tom; Got a chance to look at my mirror. The back edge of the mirror mount (the part that physically bolts to door) lines up exactly with the back edge of the wing window chrome. Will try to get pic posted for you.