Links
It is evident from the rust trail that water entered at the steering column opening, very likely when the engine compartment was being cleaned at a car wash. The water was then trapped under the carpet for possibly weeks at a time. Finally a hole formed in the floor pan near the corner.
The damage here is very minor, particularly for a car this old.
Here is the floor pan after repairs were made.
The damaged metal was cut out and new sheet metal from a patch panel was welded in its place. Surface rust in the surrounding area was removed with a wire brush. Finally the entire area was cleaned and a protective sealer was applied.
The entire car, including the interior floors, will be painted at a later date after the planned mechanical and electrical modifications are made.
The steering column opening will also be sealed to prevent the problem from surfacing again.
The passenger's side floor pan was also treated.
Some minor surface rust was found in the bend area. Since the metal underneath was still very solid no cutting or welding was needed.
Most likely this rust was due to a leak in either the air conditioner drain hose or the heater core. Both items will be replaced as part of the restoration process.