Soft Top Rear Window Size?

This will sound crazy, but does anyone have an AMC CJ5 or CJ7 that they can measure the back window on?

The top that I "borrowed" doesn't have the back window. We're leaving for Tellico Friday, so I don't have time to order one (nor do I want to foot the bill for it, since the rest of the top isn't mine). I have a friend with a '76 CJ5. He will let me borrow the back window from his, but I'm not sure if it would even be close to fitting. Before I bother asking him, I wanted to see if you guys thought it would work. It doesn't have to be *perfect*, just something to keep the heat from escaping (assuming I get my heater working...).