Vent removal quick question

[LandonL]

Tried to get a quickfix done, followed all the intructions in my Haynes manual to remove the vent window but I can't seem to apply the step that tells me to move the main glass away from the window. I've tried as hard as I can and can't move it more than a half inch away from the vent, anyone done this that can tell me something? It's a 67 and I've heard the vents are different than all other years.