63 Dart convertible attaching the top

Hi guys.
I took my top off and cleaned up the body and uh, waited a bit to long to put it all back together and uh, lost all the documentation I made, uh, YEAH, THATS IT! I LOST IT!

Anyway I trying to remember how to secure the top behind the rear window see pictures and what the heck this piece is? Thought it was for the top, anyone know?

(My service manual is quite sparse on the convertible stuff, mostly framing.)

Thanks guys, so glad you are here!
John