What to tell the exhaust shop.

You will have to find a aftermarket intake with a 4 bbl flange. None of this is without substantial cost.
If the photo of the Dart in your avatar is what your are working on,it has mechanical linkage and will have to be changed over to a cable type. 1964-66 V8 A bodies have the cable and pedal set. Or you can go aftermarket.If you are handy you can do a floater pedal 67-up A or B body. Last 64 Dart I had I used a 65 B Body set up and had to drill new holes to mount the pedal and firewall bracket.