[Boog]

So this is a truck someone else built 10 years ago? Someone else built this engine, broke it in and parked it for these 10 years? Getting it barely broke in then parking it is suspect. Cooling problem was the reason to park it? As mentioned if that engine has some type of serpentine belt system it may have the wrong water pump on it. If it has a conventional v belt setup it may have a reverse rotation water pump on it. Lots of unknowns.
Even if the engine had a good antifreeze/coolant in it when stored some internal corrosion can still occur. I believe I would take that radiator to a shop and have it checked out, boiled out to make sure it's flowing coolant as best it can. Sitting unused is often as hard on metal parts as abusing them.
How does the oil look? Do you see any bubbles in the radiator with the cap off while it's running? If so it's time to consider a cracked head, block or blown head gasket.