It's not just the head gaskets that's in issue with the 3.0 slow. The exhaust headers have a poorly designed crossover that leads to the exhaust valves in the rear cylinders getting burnt. So yeah, avoid the V6.
If the truck you're looking at is a 4 cyl with only 100k (for real vs. roll back) on it, it's just broken in. The main concern with a 25 y/o vehicle is misc seals drying out, sun damage if it wasn't garaged and if they fluids weren't changed regularly their could be some internal corrosion issues. But more than likely flush and change all fluids, new shocks and new rear springs and you should be gtg.
The stock rear springs are too soft and the rear ends sag. You can either po-boy it by adding jeep coil springs in addition to the leaf springs, or upgrade the leafs. Google will direct you to many options out there.
