My ’57 chevy convertible has a straight body and a freshly repaired and very square frame to begin with. While the body shop had repaired and squared the frame and had it powdered coated, they were also making repairs to the sheet metal of the body. Having media blasted the entire body they were able to see many issues that had to be addressed.
The floor pans and trunk floor needed work and it was decided to replace all the floors with new metal. These were received and installed with the body kept in alignment by square tubing tacked at all kinds of angles and points to brace the body and ensure that there would be no shifting of the dimensions at all during the removal of the old sheet metal and the installation of the new.
These photos show the braces as installed and the care that was taken to get the body dimensions correct as the old floor pans were cut out and new ones installed.
The trunk lid was also found to be rotting from the inside and it was cheaper to replace than to repair, and so a new one was received and installed on the structurally secured body.
All of this is expensive, tedious and requires precision in measuring, bracing, cutting and installing the new floor pans.