66 Barracuda Quarter Window Adjustment

Not sure if this will help, but I find that sometimes the master technichian documents give more detail than the fsm. For many years they would have a "body service" training session. They did not do one of these in 66, but they did in 65. If you go to 65 of the master service tech documents on mymopar (link below), you will see that the April session was body service. Starting on page 6 of the pdf it talks about the quarter glass adjustment. The videos, although a little corny and dated, usually show more detail as well. Hooe this helps.
Browse MTSC by Model Year – 1965 – MyMopar