The wheels of a dually are different than a Class II (3/4 ton) truck. All six wheels are dished and interchangeable unless the fronts and outside rears are aluminum with plain steel inside rear wheels. I think the wheels are known as "Budd" style wheels.
I think the axles are different width than that of a Ram or GM 2500 or Ford F-250.
A dually looks real strange if only the inside or only the outside rear wheels are mounted.
If you want/need a truck to haul or tow and are in doubt - buy a dually. Far too many people buy a diesel-powered 3/4 ton thinking it can haul or tow anything. They are usually mistaken and regret their choice.
The way to make a correct choice is to first determine what you will haul or tow and then know the actual loaded weight of that choice.
Once you know the weight of your cargo or trailer, look at the GVWR and actual scale weight of the truck you are considering. Subtract actual scale weight from GVWR of the truck when full of fuel, passengers, tools, camping gear, etc. The remainder is carrying capacity.
A diesel 3/4 ton can tow heavy conventional trailers but is almost always overloaded with a fifth wheel or gooseneck trailer.
Duallies and 3/4 ton trucks make poor off-road vehicles, particularly if diesel-powered. If off-road capability is your goal a light, short wheel base 1/2 ton or SUV is a much better choice.
