I heard that it isn't a refreeshed SLR, but a car to pay homage to the Gullwing, with a 750 bhp V12, and proper gullwing-style doors. It is a AMG-only project, with no McLaren involvement, after they cocked up the SLR. Can't remember where I saw the pics, maybe UK Car
If it's an all-new car, it could just be the underpinnings being tested, like the way Nissan put a G35 shell on its GT-R prototypes. Funny thing is, Lamborghini did the same thing to the front bumper of the Murcielago LP640, and we love it, but nobody likes it on the SLR.