[dtw]

I had similar holes on my '72 in those exactly locations. I was able to carve out the cancer and get back to solid metal, fabricate patches, and weld everything back in, in an afternoon. This was with the disadvantage of being outside and under the car, which made the welding interesting to say the least.

Note that those don't look to be so much part of the floors as they are the outer portion of the inner wings and longitudinals. They are stressed members though those specific sections shouldn't cause your car to break in half. A quality repair job should have zero impact on safety/rigidity. Overall that car looks pretty clean! (rust-wise). Congrats on taking on a restoration of this caliber!