Here's the SAI assembly I bought a while back.
The hat assembly with the butterfly comes from England, and the rest of the pieces look pretty much as close as possible to the originals. The ducting is very stout and has the flat steel coil instead of the wire coil you typically get in flexible ducting. The cable is precise and smooth. Nick (Mickmate) came by and inspected the set and concurred with the quality.
This is where the intake is supposed to come in from the front.
I took this on an original CSX 3000 car last year at the LASAAC Shelby show.
I have seen some fresh air kits that allow you to take the fresh air from the front valance vent, but that would eliminate the correct brake vent. I have also seen some inserts with two duct openings that would allow you to take one to the footbox and the other to some sort of flexible ducting to the brake. The SAI assembly provides a spun aluminum hat piece that screws to the radiator shroud (inner fender well). In some cases I have seen them bolted to the panel.
I have seen a recent Kirkham fresh air butterfly assembly on the footbox and it looks to be made of some kind of clear lucite or other plastic material. Nonetheless, it is a typically nice piece as well as the rest of the system which appears to be similar to the SAI set up.