Fabricated round backing plates for the fuel level sending units. Cut a wide circle out of aluminum and used flat rivets to attach 5 single wing nut plates. Also drilled four holes to attach to the fuel tanks. Cut each backing plate into two pieces so we could get the plate through the hole into the tank. Drilled the holes into the tank and maneuvered the backing plate pieces into place and riveted them to the tank. Also drilled holes for the fuel drain, intake pipe and fuel vent. Rinsed both tanks and left upside down to drain.