Go you! I'm not much of a runner myself, but I have done the London to Brighton bike ride for the two years
I tried to factor my diabetes into my training plans. I built up the distances gradually, introduced hills etc. Worked out what worked well for me with regards to food - something that kept my sugars stable but didn't give me cramp half way through the ride! I normally have a banana beforehand, or sometimes a bowl of porridge (couple of hours before I go out). I also take lucozades and/or dextrose tablets with me. It's fairly easy to do this cycling, not sure about running though...
My sugars often drop a few hours after I cycle, so I try and have some carbs when I get back home (occasionally treat myself to a cheeky ice cream if and when I stop for a break!).
Good luck with the run and for the training!
Em