I agree that Atapattu for Arnold would be best. Arnold doesn't score quickly enough for a 7, and he doesn't bowl. Play him at 3, and take the pressure off of Mahela for having to play patiently and build the innings. Mahela plays best when he can right away start pushing singles and playing some shots. Also, SL are more likely to be 60/1 after 10 than 40/1 after 12, so Marvan can settle in and play his game. Chamara at 6, followed by Dilshan. These two seem to push each other well, score quickly, and run very well between wickets. Bowling, I would keep the same. Maharoof's batting is too valuable IMO. With the trend in this world cup, big scores and chasing big scores is going to be crucial, so being 9 deep with hitters is going to be important.