I think those tires are HUGE. //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif
Could just be the pics, but the upper bars should be 30* angled, or as close as possible, to keep the axel centered.
As for the tire moving, it could be that the upper bars need to be extended some. When it goes down, does the tire kinda roll forward? If so, make the uppers longer.
**Thats a basic description od how to do it. Lots of measuring needed**
Who is doing the bagging job for ya? I might know them or know of them.
And I saw some other pics of the notch, I see it is getting all boxed in. Good job. If the frame isn't boxed in, I suggest doing it at least 1 -2 feet on either end of the notch.