Positive caster, I think of as the steering axis "leaning back," where the upper pivot point (upper trunion bearing in an 80, or upper ball joint in an IFS/wishbone suspension) is behind the lower trunion bearing (or lower ball joint in an IFS suspension) makes the tire more apt to rest in a straight position relative to road imperfections. It also increases the natural tendency for the steering wheel to return to center after a turn.
Side benefit, with a high degree of positive caster, when the wheels are turned, you'll notice the whole tire angle back. Some older European cars have really high caster, so this effect is visibly quite obvious. Well when the wheel is turned like that, the effect is actually the same as negative camber to the outside tire in the turn (even if your camber is 0*, which is spec for a solid axle truck). Negative camber (where the bottom of the tire sticks out farther than the top of the tire, picture a "stanced" out rice rocket or VW) improves steering turn-in response and roadholding as it counters the effects of body roll, keeping the tire flat to the road surface even when the body is leaned over.
Positive caster is a good thing. And to an extent, more is better, but there is a limit. First off, in a solid axle truck like the 80, the more you increase caster, the more you point your front pinion down. This creates driveline trouble because the front driveshaft u-joints are no longer in alignment with the transfer case output. This is an 80-specific problem. Or a problem specific to full-time 4wd solid-axle trucks, I guess would be more accurate.
But if you didn't have to worry about pinion angle, a nice high caster angle like 6* is usually ideal for road manners and handling. Just this guy's opinion. As the caster angle increases, so does steering effort, so there is a happy medium in there somewhere, but it will be subjective. Super-high caster can also contribute to funky tire wear.
