After the steps you mention, if you have the fuel line disconnected to the sender and the wire off you just drop the passenger side down and rock it a bit and it should slide off the filler tube.
You may want to spray the grommet sealing the filler tube with PB Blaster or silicon lube like twice a day for a couple days before you drop the tank so it's less likely to stick to the tube when removing. Also add a new grommet to your list of parts to buy if the tank doesn't come with one.
I replaced the old tank when I got my 64 Dart (rusted through). It was pretty easy and straightforward. Just watch out you don't crumple or tear your new filler tube grommet on re-install (ask me how I know). I also put in a new sending unit and also did all new lines all the way to the carb and added an extra filter as well. In for a penny, in for a pound. You only want to do this once and you also want peace of mind about the fuel system, so it's worth the $$ to do it right with all new parts. Same with the brakes.