Vent should be separate.i believe there may be slight variation in the 78-80 and the 81-87 hp dashes.look under ,near e brake cable and door buzz,there is around 6-7 screw/bolts that secure the wiring harness in sheathing that is attached along the top that secures to actual dash and will prevent it from coming out in its entirety...this is where a extra hand is helpful,if not avail you will have to balance the whole assembly forward(trying not to damage the already 30 year old brittle dash)and affix your arm in position to remove the iirc the number 7 or 8 mm bolts,then it should be free and removable...
Thanks for the intel... I hate getting reasonable suggestions while I am working.
Makes it way more difficult to finish out the work day!