Is it a earl 04 or late build 04.
Do they have paperwork on coolant maintenance?
Does it have a coolant filter?
Has it had a tuner on it, does it have a aftermarket air intake? lots of guys who tune the truck have aftermarket air intakes and 4" exhaust. If it has both of those now odds are a tuner was on it at one point. not always but more likely.
03 early-04 had a swash plate style hpop pump that was not as reliable as the 4 piston pump that followed.
All the head bolts were typical.
If the price is right and it seems to be a stock truck with good maintenance (cooling system included) it will be a nice truck to have. Try to get a chance to start it cold in the morning when cold. (will show injector issues)
If you know anyone familiar with the 6.0 that has a scanguage or some kind of scan tool they will be a huge help for you to help determine the health of the engine.
Hope this helps and doesn't confuse you.
2006 F250 LARIAT CCSB 4X4: Edge CS2, ARP Studs, O-Ringed Heads, X4 PHP Custom Tune, Atlas40 Ficm Tune, CAT EC-1 Coolant, IPR Coolant filter, Fass-125, turbo-back SS 4" pipe, Corsa muffler, 6.4 Banjo's, 6.4 starter,DC Power 270 amp alt, 2/0 cables, Die Hard Platinum AGM, 7" lift w: Icon Progressive Coil Springs, 2008^ Carli/Deaver rear springs on fatty-daddy 38/15.50/18 Toyo's