For car enthusiasts, few four-letter words carry the same sting as r-u-s-t. The brownish-orange effects of the tin worm are enough to strike fear in the hearts of grown men, and can make others curl up in a fetal position and weep. Yet try as we might to avoid the effects of oxidized steel, it's almost inevitable that we'll have to deal with it in one form or another on a decades-old project vehicle.
The good news is that most minor (and some major) rust problems are easily repaired given the proper materials, time, and talent. When rust has severely compromised or completely eaten through a panel, it's best to cut out the offending cancer and weld in fresh steel. In some cases, a little sheetmetal skill is necessary to fabricate a patch. In many instances, however, stamped reproduction panels are available to make repairs easier. When such surgery is needed on a '50s- or '60s-era Ford product, one of the first places we turn to is the Engineering & Manufacturing Services (EMS) catalog, which lists dozens of quality floor, fender, rocker, quarter-panel, and tailpan patch panels.
Del Austin's '57 Ranchero got the media-blast treatment at Hot Rods & Custom Stuff in Escondido, California, before this surgical procedure began. For the most part, its trip to the blasting booth revealed few surprises--this was one very clean car. The one exception was the floor, particularly at the rear of the cab. This is a common problem spot on these cars, as a poor factory design made it easy for water to seep in, get trapped under the carpet, and corrode the floors from the inside out. Del knew ahead of time that the floors needed fixing, so he ordered a pair of pans from EMS and delivered them to HR&CS with the car. Installing the panels was a relatively simple job for HR&CS bodyman Dave Anderson.
If there's a bright side to rusty floors, it's the fact that they can be a good place to practice and hone your body repair skills. As you'll see watching Dave, the work is fairly straightforward. Furthermore, floors tend to be forgiving because the sheetmetal is pretty heavy and contoured, so it resists warping. Besides, most minor imperfections will be covered up with carpet. Not that we had to worry about that on this car. With Dave in charge, the Ranchero was in experienced hands, and you could hardly tell a repair was performed by the time he was finished.
Dave began by marking where the old pan needed to be cut out, being careful to note where the floor braces were. All potential obstructions or hazards (exhaust, fuel lines, wiring) were removed or protected prior to any cutting or welding. | 
Factory spot welds attached the original floor to the floor brace and held a seam together along the doorjamb. Dave used a grinding disk to remove them; spot-weld drill bits are also available for this task. | 
The bulk of the old pan was cut out using a cutoff wheel on a pneumatic die grinder... |
...Again, care was exercised to avoid cutting through the floor brace. | 
Dave used an air chisel to break through any spot-weld remnants and separate the remaining chunks of floor from the brace and doorjamb. | 
The floor looked like this when Dave was done cutting. Fortunately, the floor braces on this car were solid and did not require repair. |
The floor brace was thoroughly cleaned and its edges prepped for welding by scuffing them to bare metal. A chemical rust treatment was applied to the light surface rust on the rest of the brace. | 
Like most good replacement panels, the EMS piece came with a little extra material on the edges. Dave took his time trimming the new pan and the existing floor and mocking the parts together for a good, precise fit... | 
Like most good replacement panels, the EMS piece came with a little extra material on the edges. Dave took his time trimming the new pan and the existing floor and mocking the parts together for a good, precise fit... |
...Care and patience here will pay huge dividends on the finished repair. | 
When he was happy with the fit, Dave drilled holes to use for welding the pan to the floor brace. Holes were also drilled (punched, actually) every few inches along the pan's outside and rear edges, where it would overlap existing metal. | 
A dozen or so sheetmetal screws temporarily held the new pan in place and kept it from moving too much during welding. |