Lookin' good! Make sure you fence the area in front of the tires, significant gains to be had there.
I assume you're going to use a couple turnbuckles to support the load? I agree with Arek; it won't take the load without them.
Does your mounting system allow you to adjust the angle of the splitter/diffuser relative to the ground? Another useful feature would be to have additional .5" and 1" foam spacers so that you can adjust the height of the splitter above the ground by swapping them in/out.
Looks slick with the e36 bumper and wide fenders!