I would stick with the OEM size. You may run the risk of changing ratios for the 4wd, but I doubt its enough to be concerned about. What will happen is decreased traction in muddy situations. I realize that size can be hard to come by. Check out Miller Tire. I believe they have a website and will send you a free catalog.
These are Firestones and are mounted for 200 for the pair. Its a great deal but I'm running four tires on the rear. So after all that its a no go anyway.