A 56 Buick wouldn't have ball joints. Instead, it uses the older style spindles with kingpins. To change the ride height significantly you need to modify the spindle support or "upright" as it is sometimes callled.
As the uprights carry the entire front end weight, this modification has to be done by a certfied welder who knows how to do a proper job on them. It was much easier for most builders of gasser-looking street rods (and I suppose real gassers, too) to change to the beam axle and leaf springs instead.