All right, there she is! Looks like a great project. I'm not really up on cars of this vintage but if you haven't got a factory service manual for it yet you should get yourself one.
First step in removing the tank would be to empty as much out of it as possible, if there's anything in it at all. There should be 2 straps that support the tank that are on hooks at the rear and a couple of nuts on threaded rod at the front. First off spray that threaded rod and nuts down with some PB Blaster and let it soak while you remove the plumbing and the electric connection. Next remove the nuts and the straps will follow allowing you to slide the tank out from under the car. Be smart with jacks and jack stands to support the vehicle while working under it and if you have to work on the car by yourself make sure others know what you're doing and when you're doing it. Have cell phone within reach.