Muddy - I was under the impression this was the first official running of this race. Other races may have been organised in the past, it would seem odd that it took this long to think of it! I have looked at it but it clashes with a trip I have already in the calendar.
In terms of doing it over 2 days then you have the ideal time to train for this, a weekend!
you can simulate the race pretty easily, even if not necessaily the full distance. Other than that concentrate on putting in steady miles during the week and getting off road where possible. I like to do some speed work to during the week which I find is good for helping to build strength in the legs. (for example : 30 min steady run, 5 x 1 mile reps with 90 secs rest, 30 mins steady run)
In terms of what to do overnight, just take care of yourself. Make sure you get stretched off after day 1, a massage if possible (make sure it is light), get washed etc, fed as early as possible (and drink ofcourse!) and then rest.
In terms of during the run, eat plenty and drink enough. Keeping in good condition on day 1 will help you into day 2. Little snacks that are easy to carry that you know your stomach will be ok with (try this stuff out on your longer training runs).
For kit, wear what works for you and what you are comfortable running in. Whatever you choose make sure you have trained in it before, race day is not a good time to find out something rubs!