The stuff you want to remove is the panelling that you can see when you open the trunk and look in towards the front of the car, its right behind the back seats.
Believe it or not, the fuel tank is DIRECTLY behind the rear seats. The sender unit is only accessible from the trunk. The fuel tank is like a tupper-ware sandwich container on its side, its as wide as the car, about 1.5 feet tall and about half a foot thick. And its right inbetween the back seats and the trunk (the space between the back seats and the trunk space is roughly half a foot or so).
btw. The nut/hex screw for the sender unit is a 46mm socket, but 1 7/8" will fit fine.