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You are aware that double adjustable means that they control the dampening force on both jounce and on rebound with a two variable orifices in the shock's valve body to limit oil flow into and out of the mono tube reservoir? Double adjustable shocks can be regular monotubes or coil over in construction. They are almost exclusively used in automotive racing as opposed to cruising.
A coil over shock can adjust the ride height up to one and a half inches either up or down in addition to any other device to raised or lower the vehicle. So you can lower the car with a two inch lowering steering knuckle (that raises the spindle two inches above the stock height). Add to that two or four inch lowering springs and you could knock off five and a half inches below the stock ride height with the addition of coil over shocks. Or you can lay the frame on the ground with air bags. You can similarly raise the vehicle with coil over shocks lifting blocks axle over spring kits and other bolt on's if you want to convert your Impala into a dog retrieval and bird hunting 4x4. Depends upon your goals.