Truck Repair: n-14 red top, head gaskets, oil leaks

Question
the truck i am purchasing has 612000 what is normal mileage for a in frame  anything to check for that would be a tell tale sign of a problem

Answer
Supose to last a million miles before overhauls but most dont make it for other reason than being worn out or using oil.Coolant lose would be one thing but usually head gaskets fix that,oil leaks on drivers side from camfollower bolts being loose is about the only 2 problems the N14 gives.