It has been 8 years since I installed the Targa glass into my 80SC but I was asked to post my thoughts on how I did the dirty deed, Unfortunately no pics.
There are rarely any new ideas, usually someone has already thought of it. All I did was take someone else's idea and modified it for my own purpose.
First off, thanks' to Bob Kontak for digging up an old post from 6/2003 on the Targa glass install.
http://forums.pelicanparts.com/porsche-911-technical-forum/114302-quick-targa-window-install-trick.html
The above post helped me with doing my glass install. Unfortunately, I did not heed the warning about installing the trim into the seal before installing the glass into the car. My only excuse at the time was I was in a hurry moving from SoCal to NY so I had no time to spare fiddling with trim. I still have the original trim stored away in the garage for the next time (maybe).
My wire harness at the time was out of the car so I was able to make the connections and drape the wires into the appropriate seal slot.
My bright idea was to use the straps as noted in the attached post but I did not want to anchor them to the garage floor. I had no seats in the car so I ran the hooks into the car and used the driver and passenger seat rails as the mounting points for the straps. I used a couple of thick bath towels to protect the new paint on the exterior body.
The seats are easy to take out (only 4 bolts each) and it gave a lot more room to get in and out of the car.
I did not use a thick rope, Instead I used a thinner nylon rope but I wrapped it into the seal twice. I started the rope at the bottom middle and wrapped around the glass twice. The two ends were located at the bottom middle.
You might say why did he do that??? My thought process at the time was if I did not get some of the seal over the flange on the first pass I would have a second shot at it without removing the whole glass to reset the rope. I did not have an upholstery hook so I took an old thin screw driver and bent it into a slightly curved hook and filed /sanded it smooth so it would not damage the seal.
I used dish soap on the flange and the seal. In my case I went with installing the lower seal on the flange once I put enough tension on the tie down strap to hold the glass in place. It was a slow process but working my way around the bottom on both sides a little at a time I was able to get it to seat in. The second pass of the rope was just insurance in case anything was a miss.