Well, the 69 tank is a little different, but what I did on my 68 was this...
first, unhook all of the sending unit wires... the ground shoule be connected to the underside of the trunk floor just forward of the tank, the guage wire comes through the trunk floor (behind the filler neck). For this one you have to push a grommet type thing through the hole in the trunk floor.
Pop the cap and disassemble the filler neck setup. On a '69 I think the filler neck is welded to the tank, so maybe just pop the cap?
Then, undo the rear retaining bolts. They are really long and you may need an extra long socket to get them. Support the tank with a jack and a block of wood. Unhook the rubber line that connects the sending unit line to the tank to pump line, and slowly lower the tank and pull it out the rear.
Unscrew the front screws on the tank straps and pull them out. They kind of hook onto the floor supports.