Probably. I think that all the Sunfires had the split folding rear seatback. But don't quote me!
in the trunk or under your back seat
There's a black cord inside the trunk on the top left.
Yes, the back seats in a 2004 Sunfire do fold down. There are straps on the back of the seats that are used to pull the seats down. The straps are assessable through the trunk of the car.
look up under the back window through the trunk and you will see them right there.
pull the lining of the trunk away from the back of the trunk
If you mean just the bulb, they are accessed from the trunk. Pull the carpet away from the back of the car and untwist the bulb holder. Replace the bulb and screw the holder back in.
Drums and shoes.
it at the back of your gas tank
The trunk capacity is roughly 9 cubic feet. It's not much, but you can fit 2 sets of golf clubs back there.
6 x 9
I'm guessing that you're referring to the lamps that light up the PONTIAC name across the center of the trunk lid. You access those lamps from the inside of the trunk lid IE: the back of the PONTIAC name. Mine were pretty stuck in place, so I ended up removing that entire rear light assembly. It comes out with about 6 screws. That gives you more access to the connectors.
From the trunk.