The glass is held in by two bolts through the bottom of the glass, inside the door. Remove all the window cranks and door handles (need a special tool to remove the clips, you can get one at any parts store) and remove the arm rest. Then take the whole vinyl door panel off. Put the window crank back on without its clip and raise/lower window until you can see the bottom of the glass where the two bolts are. They will have large washers on them. Have a friend hold the glass while you remove them, or proceed very carefully. The glass should slide right out the top. As to whether or not the glass from a fastback will fit, I would call an auto glass place and see if they get the same part number for both cars.