What's your starting point? If you are knocking out 60-70 miles pw, and include hills in the training, then you're pretty likely to get round on that. If you want a quick time, then lots of long runs and time on your feet.
I did it last year. I fit the above, and got round fine. Longest run I did was a support of leg 3 3 weeks earlier. I also did Edale Skyline in the March. Other than that my furthest runs were around the 10 mile mark every so often. The thing that got me round was I was having a laugh with some great people.