Dennis is right on the money with tires and sizes. I have run 20" Sand Stars and Sand Sharks on my 350s. Great for excelleration and climbing, but down on top end. Still plenty fast to get yourself in trouble though(double endo for instance) LOL.
When you pick rims, go with aluminium .190s. The lighter ones(.120,.160) bend easier when "bad things" happen. Beadlocks also help keep sand out of the beads and the air leaks that always come with low air pressure sand riding, but are expensive(on my military pay).
My 2 cents,
Gary