Floor Pan Questions

That floor's rock solid where I come from!

Maybe at some point in it's life it had an owner drill the floor for some non-original seats? Maybe massaged the floor a bit to clear. Just a hunch but I've seen it done often enough that it's a possibility.

Removing the whole floor pan is gonna be a matter of drilling spot welds then re-welding and seam sealing in the new one. The car should be supported as it would be sitting on all 4 wheels. (this would be a good time to install subframe connectors if you want em) If it were my car, being a northeasterner not only would I throw a party for finding a 40+ year old car with a floor still in it, but I would just patch up those small holes and hammer it back straight rather than go through replacing the whole thing.