Thank you!The 1957 suspensions are pretty good stock. Just make sure that everything is in good shape. You can change to stiffer torsion bars and shocks for better handling. If you don't mind a little harder ride, you can use polyurethane bushings to stiffen it up.
The ONE exception to the UniBody change was the D-car Imparials, which kept the 1957 chassis until the end of the 1966 model run. Then, Imperial was UniBody like other C-body cars, but with some Imperial-only items, for 1967 onward.Mopars went to unibody in 1960. Most cars were full frame vehicles in the late fifties including Ford and GM products. Mopars were the best handling of the big three.