The floors aren't factory or even repop replacement panels, they're done from scratch. That's not a horrible thing if it's done right and this looks to be pretty well done. It all depends on what was done inside, and what gage material was used. A lot of the stiffness of those panels comes from the fact that they are shaped and these are not. But, if you use material that's a few thousandths thicker then it will be plenty stiff. And yes the frame rails should go further back, but if they are tied into cross frames under the seats you aren't giving up much stiffness. They're supposed to go back to the rear seat bulkhead and that's how they help the stiffness, but in reality they don't do much as they are getting to a small cross section at the back end.. Also it depends on what was done to install the seat rails and what stiffening structure was put under the seats. Without seeing what was done inside there I'm not ok with it, but if it's done properly, then it's no issue at all. Some pics of the work during restoration would clear things up. As I said above, the work appears to be done by a competent sheet metal guy and that's a big positive. Lastly it wouldn't take much to fix it, some properly bent sheet and some welding would make it as good as new or better.
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