Sounds like you want a mild touring suspension- good ride quality, good stability and drivability, nothing extreme, and not slammed on the ground. Your stock setup isn't far away from that with a few tweaks, and it's not expensive to get there either.
A mild drop with spindles and rear drop springs will work to lower the center of gravity and help handling. Up front, KYB Gas-A-Just shocks are great at controlling body motion while keeping good ride quality. Add an OEM C30 sway bar, or an aftermarket bar if you're not into junkyard scrounging.
For the rear you'll want oem style soft rubber trailing arm bushings so the T/A's can pivot as designed. Stiffer bushings bind easier and will not allow the suspension to pivot freely, which is bad for ride quality and handling. Use 3" drop springs to match the front spindles. The biggest improvement you can make in the rear is to relocate the rear shocks to the outside of the frame and standing straight up and down, closer to the tire so that they can control the body motion more effectively. This can be done using your existing lower shock mounts for the cost of new shocks as shown here starting at post number 11-
http://67-72chevytrucks.com/vboard/s...05&post4730005
A rear sway bar from an 80's F150 or Bronco is a near bolt on fit with only the brake lines needing to be slightly bent to clear the mounting brackets. These can be found pretty inexpensively at junk yards.
More modern alignment specs will help with stability and handling as well. Use the caster mod described here on the forum for more caster adjustment range, and shoot for at least 5-6 degrees. -.5 camber and 1/16" toe in will work very well.
A CPP 500 series quicker ratio power steering box will make a big difference in how it drives- spend money here instead of on an aftermarket shock relocation kit.
Your stock control arms have superior bushings to the later 73-87 rubber bushings, so keep and rebuild them if needed.
Stock discs/drums will be all that's needed unless you're racing or pushing it hard in the mountains on tires that are sticky enough to overheat the brakes. Most street tires aren't going to be soft enough to take advantage of upgraded brakes that clamp harder- they'll just lock up the tire easier. Ultimately the tire you choose will determine how well the truck stops, and your driving style will determine if you need brakes with better fade resistance.