On my '73, the large windows had an inner pane that was plastic and removable. On this photo, you can see that the foam seal has deteriorated around the edges. It also looks like they have used some sort of film on the inside, hence the purple color:
IMHO, there is not all that much insulating value in the second pane, so you can just remove them. there will be some small screws on the sides that you just need to remove and then the inner pane comes out. The outer pane is held in with a permanent rubber gasket, there have been threads here on replacing that gasket, but it generally involves splitting the frame so everything can come out and then getting it all back together.
You can see where they split the frame in this photo:
The vista views or stack windows (the narrow skinny ones) are mostly held in the same way. The outer frame is riveted to the skin and the inner window is held in with some sort of bedding compound. On mine it was vulkem which was fairly easy to clean up once the glass was out. The inner window was held in with a kind of split trim ring that wedged it against the inner frame. You have to take the inner trim off first then it will make much more sense. Generally they have some sort of half silvered film that breaks down over time and looks like what you have here:
Take a looksee here around post 12 and you can see what I went through with windows this year. http://www.airforums.com/forums/f46/...or-127619.html