The suspension on the 73-87 Chev's is about as easy as they get to lower. The control arm / spindles front end can be lowered with spindles, coils or control arms up to 5 inches.
In the rear these trucks have a standard parallel leaf spring system and riveted hangers. A shackle will get you an inch or two, a hanger / shackle combo will give you 4" and a flip kit can get you about 6 inches. Of course we stock it all.