Need help installing A/C vent under the dash in '77 car
 

I have a '77 911 and I would like to improve air conditioning by installing a new vent under the dash near the console.

Currently, my car does not have any type of (bow-tie) a/c vent under the dash. I am planning on drilling a 1,25 inch hole there, but I am not sure how to connect a new vent to a/c ducts. Or is just making a hole enough?

Has anyone done this in an older car? How should I do it? What parts do I need (if any)?

Thanks