Sorry I missed your question man, I know I personally haven't been checking this forum much since it was kidnapped.
You should go with 4.75 BS on the 8" rims if you're talking AR-767's, they'll fit fine but stick out about 1/2" more than stock...partially due to the BS, and partially because you'll be moving from a 7" rim to an 8" one.
Here is a picture of Will's truck (actually a closeup of a messed up 767) w/ 31's and those exact rims (damage from a night of rock crawling back in February.) He's since moved on to 32x10.50 TSL Radials, which wouldn't fit in the wheelwell w/ these 767's (he switched back to stock.) This pic doesn't help much but if you look REALLY close you can see how the wheel is just a bit further out than stock.
