I'd take the truck bone stock original with a 300 six or 360 and NP435 over that anyday.
If that truck was a 4x4 crew to start with and had a decent body the guy that hacked that up should be shot (to put it mildly).
If you like that truck and are considering buying it check the workmanship very carefully. I've owned lots of old trucks (dozens of 67-72 fords) and done plenty of EFI conversions and diesel repowers with them. I do good quality work and will honestly say that the nicest older conversion truck will rarely fetch a penny more than a very nice original when it comes time to sell. If the install was a hack (BTW, it would be extremely difficult to put that body on an '05 frame and have things look right from underneath) the value of the vehicle is in the toilet.
If you want the truck and it's not a hack politely offer him half what he's asking for it. He'll probably laugh at you then call you back in a month Yeah, an '05 6.0 PSD is a 30K truck, but a non-rebuildable wreck of a 6.0 PSD truck can be had for under a few grand. The parts under that truck are nothing to write home about. The paint job and wheels are frightening.