How abotu try drawing a picture or using crayons or a camera shot maybe...
the Mustang dash is not the same as the Falcon and I don't think it will fit worth a damn.
It is pretty darn close tho
The only differences that I have seen in them are:
upper dash pad eyebrows----spotwelded to a flat dash
minor contour changes in the dash only around the glove box and the instrument pod.
Too many of the same parts used on the Falcon and the Mustang for them to be too different.
I have considered this very thing,----but that is about as far as I got.
If all of his upper dash is good----should be no problem to reface with a Mustang dash.
This would keep him from having to split the welds at the windshield.
I would put the Mustang face on----but leave the dash pad eyebrows off.
This would look like some sort of weird Falcon dash.
"Hmmm, looks like a Falcon dash---but something just ain't right"
(Those are the coolest modifications----the ones you just cannot put your fingers on)