For a vehicle with a leaf spring suspension, there are three ways lifts are accomplished to gain wheel clearance for the body:
1. add spacers between the frame and body
2. use longer shackles - the straight pieces of metal that attached the spring ends to the body
3. add blocks between the springs and differential(s).
You will see any and all combinations of those three mods on lifted trucks. There are also re-arched springs as well as additional leaves inserted to gain just a little more clearance.