I'm with Ken Cross - "it depends" - and in this case, largely on what you consider an acceptable result. Looks to me like your sole is plywood w/ T&H veneer, but correct me if I'm wrong. If it is, that gives you about 1mm of material (T&H) to sand to an acceptable state and then refinish. That isn't a lot to work with but maybe worth a try. Your other pictures show that the plywood is separating on the underside. Common for production boats of the era as they didn't epoxy/seal the floor boards. So really 2 issues to deal with. As long as the unevenness of the bottoms doesn't prevent the floor boards from being reinstalled securely/evenly, you can probably live with that since it will be out of sight.
If the boat is in good shape otherwise, and I intended to keep it, I'd put the old boards back for the remainder of this season and replace the entire floor with new T&H plywood over the Winter. Largely this opinion is due to certain issues I have surrounding OCD, so YMMV.
Either way, good luck and let us know how you make out.