Funny you should ask, I spent a good part of today fabbing one for my 62 dart. I started with a black 1/4"x8"x68" piece of ABS. The center is now necked down to approx 6", it will be at approx 25Deg angle, and curve a couple of inches at ea end. I'll take a pic tommorrow of the unfinished install. Theq 62 has 2 rather nicely place removeable plates somewhat behind the bumper, but the air dam will I believe redirect a decent amount of air by these, and I will be installing brake ducts, because I want to, I plan on driving it hard, and if air dam works well, it restricts the normal air to to the wheels. On mine, I also almost blocked off intentionally the entire grill with very fine SS screen, and I need the dam to redirect air into the radiator. Anyway, anything in this application can hardly hurt regarding High speed front end lift/lightness, drag is another matter, but I feel warm and fuzzy all the sudden

Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.