I cannot say for sure what may have been changed before I bought the car in 1996. My car is an early (January 72) pre-L model. I have heard that the tank may have been replaced, as fuel leaks may have been what prompted the original owner to sell it. I am the 4th owner.
Here is a pic of what it looked like when I took it out for refurbishment. The sender unit to the left has no provision for fuel pick up. The filler neck / cap to the right is original as far as I can tell. The center piece is the fuel pick up & vent assembly. It was held in place by 3 rivets. After removal, I found locating notches under the flange, and a reinforcement ring spot welded to the inside of the tank. This is somewhat visible in my first photo, and is almost certainly factory. The only thing I changed was to install Riv-nuts in the rivet holes, so the new assembly is held in by screws.