8" widw would be about as far as you will want to go. Anything wider will put the centerline of the wheel far enough out to really mess up the scrub radius and handling, never mind that it might look a bit goofy. I would suggest a 15x8, speced for a pre-'87 GM 4x4. that will keep you in the correct backspacing for clearance. use caution if you decide to go with 15x7s, seems the manufacturers only make them for Japanese trucks, those use a different backspace. While they will clear the tie rods, they will rub the drag link on a hard left turn. Also, on some wheels, the center caps won't fit right if you go with the 7" width. I know for a fact that the American Racing Smoothie is that way.
BTW, I'm running 15x7 GM Blazer Ralleys with 30x9.50x15 C range Michelins, they fit very nicley, and it still pulls hard with the 3.90 gears, but cruises nicley in high gear. Ride quality is exellent, considering that it's a truck (mine has the 3/4 ton rear spring option).
