To remove the headlight and wiper switches, first you'll need to remove the knobs. They're spring loaded so if you stick an opened paperclip into the back of the knob on the flat part of the post and push forward,that should release the tension on the spring a pop the knob off. Then,you'll need a pair of snap ring pliers. Use them to turn the bezel off the front of the dash. You should see two slots in the bezel...insert the tips from the snap ring pliers into the slots and turn counter clockwise (lefty loosey). A pair of long, thin needlenose pliers will do the same thing as the snap ring pliers.
The wiring harness for the interior post lights does run up the door frame and inside the headliner so it'll need to come out to get proper access to the harness.
And yes, you need to drop the tank to get to the sending unit. On the 47-50 cars, there was an access door, no such luck on the 51-5 cars!
Hope this helps!