Jim (PKSAM2) provided the forum with some great feedback/write-up when he had to replace the plenum behind the dash on his truck. It'll help get you to where you need to be:

https://www.ford-trucks.com/forums/1...placement.html

Don't forget to reference the pics in his gallery:

https://www.ford-trucks.com/user_gal...5&albumid=6718

P.S. I can fully commiserate with all those people who've had to pull a Ford dash in order to replace a critical climate control component. When the blend door actuator on my SHO failed, it took me the good part of a weekend to replace it. HERE is my story on that if anyone's interested.