So, as some of you may know and remember, one of my goals in ZONKEY's restoration in ~2000 was to reduce noise and heat with a dual pane rear window. And, while I was at it, to make it removable. So, I took my original window to a local auto glass shop and had them cut two versions. One was the same size and the other about 3/8 (10mm) larger all around so I could use the std "lip" of the opening. The std glass is "safety" glass (laminated with a elastic layer) so that's what I used.
I don't know about the later cars, but mine (1549) had a not quite flat rear window opening. The std rubber, I suppose, took care of the non-flatness, but with a dual pane that didn't seem to quite work. So I cut off the ends which were a fair bit "out of plane", as shown in this picture,http://home.earthlink.net/~rlb...a/catpix2/index.html
(scroll to the bottom)
Here's a detail of how I hold the ends in. The stainless steel triangle is matched by an aluminum piece epoxied to the outside of the window opening and tapped with 10-32 threads.