First he needs to be aware that there are a limited number of models of 5th wheels that would fall within the ratings of that truck, both from a payload rating and a tow rating. Short and light.
And that engine/diff are not going to do very good towing, especially if he gets into any kind of grade and/or high winds.
The short bed will probably need a slider hitch. Manual sliders are not overly expensive. Auto sliders are. Mounting should be according to the hitch installation instructions, not someone's off the wall comment.