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In my humble opinion, FORD makes the best floorpans available. It is still possible to find good donor cars from the southwest if you look.
Most restorers today would prefer this route instead of the random mis-fitment of replacement panels. Often times a good metal worker can weld in the donor panels, leaving the original spotwelds intact, making the replacement undetectable in most cases when done right. Most aftermarket panels will work too in a pinch but It is strongly suggested when doing so, to be an expert welder yourself or to have a pro welder/metal worker do it for you.