i would really recommend trying a search on this topic man...there are a ton of threads about it. It will depend on your wheel size and backspacing and whether or not you would consider beating the inner fender, flipping the quad shocks and/or rolling the fender lips.
If you have air bags, then you might be able to go bigger than most. I know HissingCobra has 295 bfg's on his 79 and he has an air bag on one side to keep from rubbing. You'll prob. want a 10" wheel with 6.5 backspacing.