A few day ago the forum discussed the parts numbers and the installation of a Saturn air deflector (Part # 21031161) on an Avanti.
I just finished the installation on my 83 and used a couple of tips posted by Gunslinger.
I used a 1" X 1/8" flat bar to span from end mounting hole to end mounting hole and installed it in the bottom of the radiator frame with 1/4" bolts.
After the install, I was not happy with the look as the deflector is about 6" wider than the radiator frame and just doesn't look right. So I made a couple of filler plates to fill most of the gap and also support the ends of the deflector.
Here's the pictures.