That wing is the DGP/IRM wrap-around wing for the notchback cars.
There are at least two different versions. One version only goes half way down the rear of the decklid, while the other extends all the way to the bottom edge of the lid with a hole cut for the lock.
The original was made by DGP while they were producing the IMSA race bodies, and after IRM bought their molds, another was made with the different configuration.
) have both sets of molds, and have made quite a few wings from both types.
If you think you might want one on your car, and can snag it cheap, I'd advise you to do it, as either one sells for over $300 new. Even just to resell, if you can get it cheap enough.
[This message has been edited by Sage (edited 07-03-2014).]