i have done it by just letting down the shocks, but it was not easy. getting the tank out and in was a huge pain and i would suggest taking the rear either out or disconnected from the lower control arms.
but if you only want to lower the rear you have to drop shocks, panhard and upper panhard bracket.
I just did it on my 02 Z28 without droppin the rear. was my first time and it took me literally 45 minutes to an hour...w/the help of a buddy supportin the tank. its not bad as long as you take off everything. Panhards...both of em, heat shields, gas nozzle.....think thats the jist of it. dont forget to disconnect the fuel lines and wiring.