[jdurant]

The outer edge of the wheel would be 3.5", or 4" inches from the mounting pad of the rotor depending on how backspacing was measured. Because a 6.5" rally actually measures 7.5" from edge to edge. So your 8" rally should measure 9" wide.
Just so you know they did make a 7" rally, therefore it actually measures 8". And the extra 1/2" is on the outside. They are kinda hard to find, but I think that would make for the best combo. I think they were on some of the earlier trucks and I think I have seen them on a few vans. Supposedly all rally wheels are stamped on the inside with a size.