Your question can only be answered by knowing the loaded pin weight of the trailer in question. You would also have to know the payload capacity of the truck in question. You would also have to specify how much weight you were adding to the truck with family, pets, gear, generator, FW hitch, etc.
If the weights work with a SRW then by all means use one. But, if the weight is too much you'll need a dually. Either way, a dually will provide a significant safety margin and allow for a larger trailer in the future.
As for a Ford 6.4L diesel, I wouldn't take one if it was given to me. They are known to being rather thirsty. They are also problematic and very expensive to repair. Our boss bought a '10 Ford with the 6.4 because he got a "good deal" on it. It had to go into the shop. The least expensive repair option was an $8,000 dollar engine replacement. He just scrapped the truck and bought another one since he only paid $10,000 for the whole truck.