Awesome find! Bad news is that 14" of salt water is enough to get into some hidden gaps in the 911s structure (like the rocker panels and inner doors) and feed the tin worms that likely had started eating already.
Even if there is no rust outside it will eat your car from the inside out like a cancer.
I would strip out the interior and give the car a good dousing with a power washer, obviously avoiding the dash and electricals. Drill small holes under the areas shown by techweenie in the below thread and pressure wash any areas you have access to. Then use compressed air and then the air ducting method described above to dry things out. See this old thread about another Katrina car:
http://forums.pelicanparts.com/showthread.php?t=242536&highlight=flood
Best of luck...the polo red with ivory interior should be a real beauty when done!