Ask the local police? I dont think there are any on there for inspection laws. Actually, my truck didnt come with them so I honetly dont think you need them. As long as the tire sits inside the wheel well your good. 
You realy don't want to be any closer than 6" to the ground. That's when you start backing into curbs and parking lot bump guards with them. 7" off the ground should be plenty to stop it all. Make sure they are wide all the way down. It doesn't do any good if they get narrow down below.I guess that's a good point....my truck didn't come with them from the factory....but then again I think that 265/75-16's are the biggest size that GM considers acceptable. My thing is....I have the biggest/longest mudflaps that I could find from an aftermarket offroad shop, and I still have like a 6-8 inch gap from the ground that sprays vehicles behind me...oh well. I guess we'll see how daring I want to be.