Hi Running Rodent, yes, I'm intending to do Croydon 30 on my way to NDW50 the following month. Okay, the two schedules I made use of/adapted are:
http://www.runforthetoad.com/trainingprogram.html. Advantage: it starts from weekend "long runs" of only 6 miles /10 K. Disadvantage: It's in kilometers; you need to convert to miles. Also, the second long run gets up to 15.5 miles, so you HAVE to get them in Saturday & Sunday unless you have a lot of free time on a Monday.
I started 21 weeks before the race and used this to about week 11 (except not doing the hill intervals, just a run of 7-8 miles). I then switched to:
http://www.trailrunevents.com/ul/schedule-50k.asp (Ultraladies (and Ultraladies Men) 50K Event Schedule. I couldn't have used it from the start, because 21 weeks from the London Ultra my longest run ever was about 14 mile, I was training for a HM, s and this schedule starts with a long run of 16 miles, then 18. However, once my LSR mileage was up, this was good because it was giving me every other week as an "easy" week, reducing the risk of overtrainig, and since I was nursing a hamstring niggle... Also, the second of the long runs was only 10 miles, which I could fit in by taking a two-hour lunch break, the weeks where the main long run ended up being Sunday rather than Saturday.
I didn't get the midweek long run past 8 miles, but I made the two either side about 6 miles each - so about the same mileage.
I didn't worry too much about matching the schedule exactly, but I made sure I'd done 20,22,24,26 and 27 mile runs, with a 10 mile run the next day, and I tried to run three days midweek but have the day before and after the long runs off - except when I did a parkrun the day before the long run, or....
Flexibility! But do the long runs. I intend to base my NDW50 training on the Ultraladies 50M schedule probably combined with a Comrades schedule I found.