I have to remove a window on my '64 Bambi II and I know exactly what you are talking about. All I did was bend the eyebrow up slightly, just enough to get a screwdriver in to loosen the set screw. Once my broken corner is welded and the window put back together, I will slide the frame in, replace the set screw, and bend the eyebrow back into position.
Hopefully this process will not leave too noticeable a crease in the thin eyebrow metal.
"The difference between vintage and retro is that vintage is honestly old and cool. Retro tries to be but isn't."