looked at that schedule again, and i can't really believe it. so for a 50 mile race, they recommend (on average) 50 mile weeks!? kerraazzzeeeee.
you'd be better off building to something like a slow 25 and a slow 20 mile run every week, a medium paced 15 and a tempo-paced 10. that should prepare you pretty well. step back every month or so.
i was doing (usually) 1 x 25 and 4 x 15 miles a week buiding up to a triple ironman recently, and i completely kicked a$$ on the run. the swim and bike were rubbish, but that's not relevant to this discussion! the 4 x 15 were fitting running into commuting - running to and from the train station twice a week.