In reply to Kimono:
It's too late for training to make any difference now, but...
Make sure you're comfortable on the bike - much more important than having an aggressive aero position when doing this kind of distance for the first time. Position on the bike is the most important, but using padded shorts, comfortable mitts and comfortable, close fitting, clothing will also help.
Given that you have good fitness, the mental side has the potential to make or break it. If you've not done a day as long as this in the saddle, don't think about the full distance as that will make it a lot harder. Think about getting to the top of the next hill, the next cafe/cake stop, whatever helps to break it down.
Don't let your energy levels drop. If you've done 170km days before then your body is probably fairly good at burning fat so as long as you keep topped up with food and ride at a steady pace then you should be fine.
As has been said above, 330km in 12 hours makes for a pretty tough pace! Minimise faffing and time off the bike and, if you're bonking, remember that crawling along at 12mph is still faster than stopping!
Have fun and good luck
Post edited at 12:39