I would make sure it is a Cummins under the hood at that price.
Ford used their Brazilian built inline 6 diesel engines for several years. The Brazilian 6's came in two sizes, one of which was 5.9L. They are really pretty good engines but the only place you can get parts and pieces for them is from Brazil.
For that matter, Ford medium duty parts of any kind are becoming increasingly difficult to find. Once Ford sold their medium duty line to Sterling they stopped almost all parts support. Supposedly Sterling was supposed to take up the slack, but if it is older than ten years old you are going to be out of luck.
IMHO, I would pass unless the price was less than the price of scrap.