Passenger side in the tunnel and the bottom as well as the front rail. This was cleaned with a putty knife to get the dirt/grime off and then with simple green and a brush then wiped dry with a towel...
Seems the evidence keeps building that this particular car did not get floor primer/sealer. If the floor is not rotted out, it's just short of a miracle that it's still together, lol!
If you can show irrefutable proof with pictures, I personally might be inclined to paint the undercarriage with a silver paint to replicate the appearance of bare metal. It gets complicated, though, as the frame rails and rocker panels were galvanized. You'd have a tough time replicating all the dark appearing spot welds. Would be a fun, interesting project. But, as Jeff mentioned, you're going to get a lot of critics and you'll be the 'no primer guy'... which might not be all that bad ;-)