Here's Jack's thread. The one thing I did differently on the back window is I jacked up the rear of the car about 18" and put it on jack stands. That reduced the angle on the rear window and kept the bag of sand from sliding down the glass as I was roping it in.

http://forums.pelicanparts.com/porsche-911-technical-forum/756051-race-prep-backsliding-re-installing-rear-windshield.html

Just because someone has been doing something a long time doesn't mean they are good at it.

One more thing. The rear glass is tempered, and very difficult to break. You shouldn't have a problem pushing it out from the inside without breaking it. That said, however, I made it easier by slicing the rubber seal about half way around and started pushing (from inside the car) at one of the upper corners. Once it begins, it comes out very quick and easy.

I did the front in 15 minutes . The back took me a few hours of frustration. Keep in mind that the seam of the seal goes on top middle , That helps as well .

If the seal is hard then you will need to cut it out.

I make a 2 sided cut to remove the trim on its own. Angle a razor blade on each side of the trim and it will remove without bending. Then the glass will lift out easily without breaking.

Carefully look at the way the holes are placed in the old seal and then duplicate with the new seal.
Works well.

If you take your time you can should be able to do the installation following Ed's excellent (As usual) advice.

Thank you! And nice tip!