#2, Just a trim level that sounded nice... lots of optional accessories bundled together for a low price.
For our van, I think it meant it included the cassette stereo, power locks, air conditioning, fold-flat 2nd and 3rd row seats, and a built-in picnic table (that we never used)
It probably entailed a different set of options for the pickups... maybe it was called "Prospector" because it included air conditioning, which would make sense in a desert environment?
[edit] I also realize this pickup is two-tone... our van was two-tone as well... I wonder if that might have been part of the package?
#4, Our van must have been a level III, then, since it had A/C... though, I imagine, even in '85, it would have been rare for a dealership in this godforsaken swamp of a state to sell a vehicle without air conditioning.