Air bags on the rear suspension?

[theastronaut]

Before changing springs, remove the shocks and see how easily you can compress the rear springs. The rear of my '66 floated and could easily be compressed 3-4" with the shocks removed. It may be that it has very tightly valved shocks that aren't allowing the suspension to compress/extend easily enough over bumps unless there is added weight in the back. You might be able to get away with lighter duty shocks and your current springs.