When you think about it, the cars won't change much from last year in relative terms, so blocking off the diffuser and fitting a moveable rear wing isn't too hard, fitting KERS however may be difficult though.
This to me means that Mclaren have decided to stick with a push rod setup, other wise they would be running a new car with pullrod because the differences are very big.
Just my thoughts
![Smile :)](./images/smilies/icon_e_smile.gif)