Thanks for your kind words.
Actually, both of the adjustable shutters were handmade from 1/16 inch flat aluminum sheet material. They are different because they are early prototypes. We are using the one on the passenger side as our current design .
But you are correct that a residential A/C register from Lowes can be used for this purpose as the picture below shows. Unfortunately this one was made from very thin steel and froze up from rust after only a few months.
By the way, This is a picture of the ORIGINAL Donkey CRX that Ecotex found. Notice it also has Lowes flower bed edging as the air dam material. It improved MPG by about 4 MPG.