Although there are not a ton (pun intended) of options to lower your three quarter ton and one ton classic Chevy's we do have a few options to get that classic hauler into the weeds. DJM Suspension offers a 3 inch front and 4 inch rear lowering kit using lowered control arms in the front and shackles and hangers in the rear for the 1973 to 1991 models. They also do a 5/7 drop for the 1992 to 2000 model years.
Belltech also has some options to get it down using either coils springs, spindles or both in the front. Then they do a shackle and hanger combo or a flip kit in the rear enabling you to go down up to 8 inches (on some models)