how to get back window out??

rt7413, I responded to your question a while ago but it doesn't seem to have posted so I'll try again.
As Mike said, you need some type of wire "saw" to cut through the old sealer that is between the glass and the rubber. If there's a Princess Auto store near you they sell one with wooden handles on each end and the wire in between, and I believe they are right around $10.00.
However, the first thing I would do is check the price of a new gasket, and then check the availability and cost of a replacement rear window. It's a lot cheaper in the long run to just take a utility knife and cut the gasket away from the window - VERY CAREFULLY - then put in a new gasket when you put your window back in place. It's very difficult to remove the window without cracking the glass, and the old gasket is probably toast after 40 years anyway. It can be done at home, but I'm not certain if the effort is worth the price of a replacement gasket. Hope this helps.

Mike, I see we finally got you and Socket converted to Canadian Club Whiskey. :)