First off... I didn't know you drove a chunk of wood. I'd guess any tires you nail on the side would look ok.
But I suspect you mean you have a 4x2 (aka 2wd). A 2x4 is a chunk of wood.
It really depends on the year. 31" tires will probably not fit without rubbing on anything older than a 1998. With a 2" lift they will probably clear fine on most.
235/75/15 or 30x9.50x15 tires are usually the same tire with just a different size stamped on it. Sometimes the metric sized ones (235's) are a little cheaper. They will fit just fine stock and fill the wheelwells nicely.
You also have to consider what gears you have in the truck and what motor. If you have a 4-cyl and 3.08 gears, 31" tires are going to suck big time. Actually, 31" tires and 3.08 gears no matter what the engine will probably suck. 3.73 gears work out good for the 6-cyl motors and the 235's/30" tires.