Ok, you're already starting with the right motor
and the mileage for an '03 common rail is crazy low! If you don't buy it I will!
Things to look for on the dually:
check the INSIDE tire as it's regularly neglected and has been known to air down which causes crazy wear on the tire. Cracks can form on the outside rim due to overloading as well as warping of the hubs.
Aside from that, I don't have much else besides recommending getting a full safety check done.