lol, probably doesn't really matter what kind of oil you use, they will last forever anyways.
Id suggest using some 10w30 dino for, 1, its cheap and readily availible, and 2, because it has higher mileage and would be more likely to consumption.
story here: a bunch of guys in this car club/internet message board I visit got about 250,000 miles out of a similar truck. It eventually threw a rod right through the block, yet was able to idle its way to its final resting spot a couple miles away on 3 cylinders.