Can you get a picture of the rust dangae to the cowl? There is a 73 at the pull a part here, but I don't know if the cowl is in good condition or not (it could be worse if memory serves me right as I pulled the wiper transmission and the cowl covers. On the 71-73 the entire cowl is beneath the hood. but if you seal the vents off, i suspect your vents in the car aren't going to work too well!
I can see if they would cut the cowl out for you to use as a patch panel, but they don't allow power tools on the yard.