I think your Cab & mine are pretty similar ? It's been a few years since I redid my truck, but as I recall the window / frame unit opened up wide ( full horizontal ), so you can get a screwdriver on the head of those screws. The tab of the hinge slides into a slot on the top of the frame. Are the hinges rusted up tight which is limiting opening. When you take off the header panel, you might be able to spray in some rust buster on the hinges ?
