1. The bolts that come attached to the mirror from GM cannot
be used (or at least I have not seen a way to use them)
Use different length 10 mm bolts to screw directly into the
mirror base from inside the door.
2. Put some white grease on the mirror base bolt holes, line up the plastic mirror base cover on the door moulding and press the mirror into position. This leaves grease where the mirror base touched, you now have a mark of where to drill your holes.
3. I was only able to get two of the three bolts into the mirror base from inside the door, the third one is close to impossible, short of cutting away an internal support in the door. I have had no problems with only having two bolts holding on the mirrors (2 on each side).
4. Its best to take out everything except the window regulator when doing this mod as you will need plenty of room inside the door to get your hand in and maneuver.
5. Where ever you put your hand into the door through the door skin make sure and cover the exposed metal with tape or a T-shirt as the metal can cut you (it cut me up pretty good)
6. if you are installing a interior manual adjust mirror on the drivers door make sure and cut a hole under the mirror base large enough to get the adjuster through (about 1/2 inch diameter hole).