1 ton single rear wheel, and 3/4 ton 14 bolt rear ends are the same except the size of the brakes.
A 1 ton 14 bolt cab, and chassis rear end is narrower, but internals are the same, brakes are the same 1 ton.
A dually rear end is completely different as it is a Dana 70, and same width as a single wheel 1 ton, or 3/4 ton rear end.
All duallys got Dana 70s.
All cab, and chassis 1 tons got 14 bolts.
Adding fenders to a fleet side bed will require cutting the wheel arch to clear dual wheels.