I've taken the dash outta my EB Fairmont. Once before and I've got it all out again at the momment. Along with the engine :).
Last time I had the dash out was to replace the airconditioning evaporator. Whilst doing this I noticed the Recirc Vent was broken. I suggest buying a new one from ford, or find a vent outta of a later model falcon, because these ones have a better design to avoid breaking.
From the way I look at it. You will need to take the whole dash out to replace it.
I've attached some photos...
This is the first step. A little difficult, but necessary...
This is the vent, out.
This is the vent attached, alongside the heater box.
There are only 4 nuts. However, there are wiring looms connectors and vacum hoses all over the thing.