Be advised, the toughest part of that whole job, (IMO) is the weld where the pan meets the firewall, especially the corners of the foot well. If I were doing patches I'd consider removing them from a donor car, but if going the whole floor, I'd start with a new, whole pan. It might go without saying, but I would not attempt to do the whole pan unless I had the engine and trans out, to make accessing the firewall to floor pan seam easier. Making frame connectors from 1 3/4" roll bar tubing would also work, and you could get them tacked in place before removing the floor, insuring the car stays square. and then finish welding and painting while the floor is out.