64 Dart GT headliner help

Hi all and thanks ahead of time.
I have been getting the final leg of my 64 Dart restoration, modification completed. It is coming along with the occasional show stopper, but basically almost done. I have a question on the headliner install. I got a Legendary Interiors headliner about 12 years ago and I am just getting it ready to put in. It has 6 ribs as did the old headliner. I systematically move the ribs 1 atatime to the new one. I cannot figure out where the rear most bow lives. The front and all the ones on the way back have slots in the window rail and look perfect. The final bow should hook in somewhere around the courtesy light, but I see nothing. I have read about a spring in the back to hold the back most rib in place, but I dont see it. Any help would be appreciated.