If i were you i would let autoglass or Rac do the work, i had mine replaced by the dealer a while back and they didnt bond it in properly, so i had a whailing noise at high speeds which eventually ripped the A pillar trim off on the m5, I tokk it in three times to tell them it was not right but they "couldnt" find anything wrong! I took it to another dealer and they replaced it again after a few weeks whilst trying to get the original dealer to fork out for it.
So, although, not all dealers will misfit a new screen, i would gladly let autoglass on my car as these guys replace screens EVERYDAY and the dealers technicians may be lucky to replace one a week/month who knows.
This way, autoglass is cheaper, and if it is not perfect they would have to sort it out anyway, and your not paying £335 quid for it to be done
Richard