Like IKR said, this is a "fixed" but removable panel on a real Murci and it covers the mufflers therefore it's called a "muffler panel". I've seen several builders hinge this panel since there is a small trunk in the rear of a Fiero and this panel can give you access to that space. One very interesting thing that I found was that an OEM panel is a exact replacement for the G28 which means that if you find a reasonably priced OEM panel with spoiler, you can bolt the entire assembly onto your G28 based body. I had a OEM spoiler that I was going to use with my G28 panel but rather than waste a lot of time and money fabricating that part so it works with the spoiler and is functional, I've ordered a panel from John Watson and I'm going to use my OEM spoiler with that replacement panel to minimize the fabrication (time and money in the bank).
Chris