Depends on if it's still in the truck or how much of the rest of the engine is still attached. I have steam cleaned ( really hot water ) long blocks inside and out then oiled them up before any rust could form. These were really dirty inside so it was the quickest and easies way to clean them without tearing them apart. At a bare minimum, you need to pull the sheet metal pieces ( side cover and oil pan ) and clean out what you can with brushes and scrapers using your choice of solvents. Everyone has their preferred cleaner to use, mine is high pressure hot water and Castrol degreaser.
Any cleaning solvent you use will run down the cylinder walls and collect at the top rings when cleaning the piston tops. Soft wire brushes and compressed air will minimize the crud collecting at the rings. If you choose to go with a liquid cleaner, flush the cylinder walls and oil afterwards, another reason to pull the sheet metal. Engines are really tough, it takes a really big mistake to hurt one. Some degreasers are hard on aluminum and bearing material if left to long, Castol being one of them, so don't leave them soaking to long. The old method was to use gasoline, brushes, scrapers, and compressed air.
