Most classic cars suffer from some form of rust, usually you dont even notice it from the outside, until you go poking around and find out that your chassis rail is rusted from the inside out. Take a look at these pictures from Leigh's Chrysler Valiant CM GLX, what looked innocent enough, turned out to have a poor repair job welded over the top, a complete reconstruction of the steering box crush section was required. This also greatly improved the Chryslers handling and steering characteristics.
Also to improve the safety of cars such as Valiant Coupes and Pontiac Transams, which have little middle body strength, Valigrunt will custom make and fit Chassis Rail connectors. Chassis rail connectors stiffen and strengthen the midsection of cars reducing body flex and twist.