According to eMercedesBenz, they are either testing is a new variant of the current SL (obviously the SL63 AMG comes to mind), and with the new engine, so to comes a styling revision to coincide with the rest of Mercedes' current model range. Secondly, it's possible the SL in question is simply being used to test various components of the next generation SL, much like components of the new C-Class were first tested in the previous-generation C-Class' frame.
To read the whole story from the, the link is below
http://www.emercedesbenz.com/Feb07/1...r_Testing.html