Big block spec'd front coils will have more spring rate @ the same height as a sbc spec'd spring.
The previously recommended HD front sway bar from a 3/4 or 1-ton truck w/poly bushings works well or a larger aftermarket bar w/swivel style links for less bind.
Swap the steering box for a spec built unit. One board member that knows his way around these trucks speaks highly of his recent RedHead Steering Gears C10 box swap. Check out his comments on his build thread (
http://67-72chevytrucks.com/vboard/s...444746&page=35).
Better/tuned high pressure gas shocks. I really like Bilsteins....
Rebuild everything.
Consider swapping in some of Porterbuilts tubular a-arms (Delrin based bushings & they offer much improved caster). No drop as a direct swap.
That should definitely get you started in the right direction....