Ive done some checking and it appears that Convertibles that are non ac cars did have a system called astro ventilation. I cut and pasted one persons description of how it worked. Can anyone confirm this to be correct? I do know that the glass on my doors had the original retainers on them so I am pretty sure the glass was original. The vents in the back deck area does have an actuator that a vacuum hose goes to the heater control area. Below is the description I found: Keep in mind its not my writing!
the astro vent is actuated by vacume from the
heater
temperture wheel. There is a damper on the ceiling of the rear cargo
area. thats what the grills are on the rear deck just in front of the
gas cap. When the temp is set to cold the vent opens allowing fresh air
in from the front fresh air dampers through the passenger compartment
and out the vents in the rear.
when the temperture wheel is moved to increase heater temperture the vent in the rear closes so the heat stays inside.
Rodney