Neil, that's a good idea, but I'd rather not mess with the dam and undertray that way. Instead I'm going to add the deflectors separately, so I can test different designs (hopefully with my MPGuino, which I don't have wired yet).
Here's pics of the airdam completed. There's a clearance of about 7 inches or more between the bottom of it and the road. Given, it still reduces the clearance when starting the car up an incline or going up driveway entrances or whatnot, but I knew that would happen going into this. I'll just be more lenient about going over things like those.
This one's from far away and close to the 'level' line straight forward from the car going from the lowest parts of the center of the car to the bottom of the airdam, to show how close I got to the optimum airdam height. It's not perfect, but it's close enough for me.
And a final one from Car's "bad side", that shows my first try at Bondo to repair a rust hole. I didn't like it much at all, and was too lazy to sand it.
I haven't decided what I'm going to do with the trailing edges of the airdam, on the sides, but they're out of the way for now. Next up is the undertray.