The Classic Chevy's feature a control arm and spindle front suspension making them easy to lower using either coils or spindles. Keep in mind that from 67-70 they had drum brakes on the front so if you want to use spindles you have to convert to front discs. (It's OK, McGaughys offers all the parts)
In the rear the "standard" configuration is a trailing arm and coil which can easily be lowered up to 5" using coils. But, there are a small number of these trucks that have the rear leaf option. DJM makes a hanger and shackle set up for them but its rare enough that we don't stock it.