So, my coach has given me a carb loading diet for 3 days that I'm on now. Seems fine so far.
Also - he's told me to run 3:45 which means I should be able to enjoy the marathon. I think I'm going to take the opportunity to try and run a negative split so I'll run the first half in 1:53 and the second in 1:52 or faster if I'm able to stretch my legs a bit.
I'll keep you posted.