I saw that the Sportec RS600 as well as the intercooler kit come with these lower engine shield vents. I figured I could replicate them for a lot less money, like $8.00. All it took was some 1"x1" angle aluminum, and some 3/16" rivets. First layout a pattern (I used 3/4" masking tape).
Next cut out the openings (I used a pneumatic mini sawzall, but a keyhole saw would work), and then clean up your cuts with a file.
Then cut the aluminum angle stock to fit the openings, mark your holes, drill, then rivet them in place.
I also wanted to redo those rubber brake cooling dams that were scraped off of my lower shield, so sacrificed an Impala front air dam that I found at work. It's a heavy plastic rather than the rubber that they were originally made of.