How to make defrost vents open

How can set my 1980 260 to defrost permanently
Many vac leaks in dash
I?m talking about what flap can I screw open or remove

Remove the glove box and it will be obvious which vacuum motor opens the defrost vent. Once you understand that you will have to pull the instrument panel and do the same thing on that side.

Flip through cleanflametrap.com's dash removal/heater core replacement/blower replacement pictures and you should be able to find pictures showing the defrost vents and actuators. There's a small black vacuum actuator, about the size of a walnut, by each vent.