Fit some springs in there to get it to the ride height you want, and when you want to jack it up, run it up on some 2x12's. Air shocks are very ineffective shock absorbers and will ruin the ride.
Another trick to jack up a really low car is to jack it from the side. Jack up one side and put it on low stands, and then jack up the other side and do the same. Then you can easily fit your floor jack under the front cross member and the rear axle to get it higher. It is tougher (or maybe impossible) to do with the X frame impalas, but give it a try. Don't jack on the body though!