Update: I’ve ordered a similar-ish vacuum actuator out of a modern Ford van and I should be able to modify it to fit. Time will tell.
On a drive yesterday I noticed I wasnt getting any air flow out of the center vents in my new mustang, figured it would be a simple issue like a disconnected vacuum line so I decided that would be the first thing I fix on the car. It was not simple. I tracked a vacuum leak to the heater/defrost door vacuum diaphragm which though you can easily touch it with the radio removed, you can’t service the part unless you remove the entire dashboard. That sucked so hard.
I got the part removed and it ended up being filled with seeds and nut shells, somewhere along the line a rodent must have lived in the car? Or things fell down the dash board? I dont know. Then I found out that Ford doesn’t make replacements, nobody does! I can’t find the part anywhere, not even used on ebay! So now I have the dashboard removed from my new car and no viable solutions to my problem.
I would like to commend this guy for his excellent guide on removing the dash http://poisnus.com/files/heater_core_replacement.html