The course is run on existing footpaths and (in a few places) roads so I would say to go with trail shoes. There are only a few short sections which were muddy so you could probably get away with racing shoes.
If you do go with trail shoes, then you may want some extra padding in you insoles. The image below (From the hillrunner.org.uk website) shows part of the course which is made up from large cobbles/boulders and goes on for a few miles. I found that running on that bashed my feet around and made them quite sore.
The course looks fantastic and I've signed up already, but I'm wondering what people will be wearing to carry the recommended 1.5 litres of water?
That much water would easily fit into a Camelbak bladder, but filling it during the run would be quite tricky. I don't know of a bumbag that will take two 750ml bottles, so would one bottle in a bumbag and one in a rucksack work? That seems like quite a bit of baggage to carry for a marathon. Alternatively are there any rucksacks that take two 750ml bottles (in side pockets for easy access) that can be recommended?