I generally use the rule of keeping tires to 4" wider than the wheel, or less.
Though there are lots of people running around with 10.50 tires on 5" wheels, there were also some stock 6" wheels on later EB's I thought.
But that's just the wheel width vs the tire width. Not what will fit the vehicle.
Unlifted and uncut, I'd probably stick with a 235 or 245 x 75 tire. If there is a 245 available in that size? I looked recently for one and did not see them.
I believe that a 255 wide tire would still be a safe bet for the wheel, but then it comes down to the overall dimension as to whether or not it will still fit the truck.
And then you can sometimes run into the problem of a tire store not being willing to go against their practice of only mounting tires to wheels within the range specified by the tire manufacturer.
Hard to go wrong with a 235/75-15 tire on a stock uncut.
Paul