C10,
When I bough my truck the PO had the front lowered so bad that if you turned and hit a bump, the tire would smack the fenders. When I had the front end adjusted the mech measured that he had lowered them at least 4 1/2 inches and noticed that the "bolts had about a 1/2" left.
Also if you do this yourself, PLEASE spray Kroll oil or PB Blaster all over the bolts and nuts. Let it soak a day and go back the next day and resoak the nuts and bolts. If not you are taking a chance to snapping the special shaped lock nut they used and THERE ARE NO REPLACEMENTS.
Jake