[skunkwerks]

Usually you would use 3/8 tape for the front wind shield and 5/16 for the rear
Make sure you use 3M pinch weld primer on any bare spots or after you sand rust away. Then apply it all the way around the entire pinch weld area.
There is special adhesive in this primer and helps the tape stick like it needs to. all original GM cars have this in the pinch weld area.

After install with Butyl tape use a tube of urethane to fill in around the
edge all the way around the glass.
Cut the tip with an upside-down L or 7. The upper edge of the 7 fits on the glass
and the Cut part is deep enough to hit the bottom of the pinch weld.
That will force the urethane in the area it needs to be in and get you a good leak free seal.
Do not try to clean the urethane up until it dries. Once dry you can cut the excess with a new razor blade.