Lot of rust to contend with. Why not buy a car from one of the AZ vendors? Just a shell or what ever? Here's the way I look at it. You're going to spend a LOT of time repairing rust, what is your time worth? $$$ of course. If you start out with a more solid car you'll be able to spend more time on engine, drivetrain and small body work than with the project you have on your hands there.
My first Z was in poor shape too, floors had been cut out and rivited into place were new sheet metal floors. I parted that car out, got my $600 plus out of the parts and went and found another car.
Just my .02 worth, but I wouldn't rebuild what you have there, use for spare parts or sell items but to dump hard earned cash and not to mention your TIME into it, pass.
I'm sure somebody on the board would be willing to help you find something better if you ask. Go here and see this, I know this guy and the car. It's not a steal but no rust. http://skidcity.com/phpBB2/viewtopic.php?t=201