How to remove door glass/vent window in 1968 barracuda?

Push the lower adjuster stud you removed the nut from up to disengage it from the door bottom. Remove the bolts from the rear guide and you should be able to tilt the vent frame and side glass rearward at an angle and remove the whole assembly with some twisting to get that lower stud bracket to clear the space at the top of the window channel.