Your truck was sitting what six years and it sounds like you just started driving it without inspection or service. This is not a good idea with a DD. I think you need to really get the brake system up to factory spec. before deciding if changes are needed. IMHO disc/drum is a non-problem for most people and more to the point "I want" vs "I need". Set up properly, with drums and rotors to spec. and premium pads, the factory installation will give the performance you need. Too many people shop brake parts by price and want "lifetime" pads thinking they get performance too.
Of course you will still need to address the existing problems with your system. You never addressed the apparent brake system mismatch in your last brake thread (my post #10).
http://67-72chevytrucks.com/vboard/s...d.php?t=578172
A lot of mismatched parts are never going to give you the factory designed performance and adding to a bad setup is not going to make it wonderful.
Identify, correct and then evaluate.
By your own admission you are technically weak on drum brake service. Buy a brake book and do some learning before deciding that throwing discs on the back is going to make everything just great.