Its sounds very realistic,especially as you have eight months to train.Plenty of long walks with several back to back 20 milers at weekends and shorter walks or runs during the week.Aim to hit a peak of 50 miles a week in the final few weeks of your training and then back off during the last couple of weeks.Most important thing is to want to see it through and being determined not to give up whatever is thrown at you,weather,pain or just completely fed up.