The Impala has beefier springs because there is usually another thousand pounds of car over top of what a Chevelle weighs. Other than that disconnect the shocks and pull the drive shaft and the rear end can fall free without a lot of drama usually. I use a screw jack under the rear end with the car up on the rack, but a floor jack should do the same thing if you are working on the garage floor.
As always safety first. Eye protection and strong stable jack stands to hold the car up. Only use the jack to lift the car.