As with all runs/races, there's running it, and surviving it...
My old man has always said to me that to do well in a marathon, you really need a year of marathon specific training... Which I think is probably fair enough if you're really focused on getting a good time... If you want to survive then obviously you can get away with a lot less.
If you're thinking of entering FLM next year though, I think with a year's training you should be able to run it comfortably, and then perhaps continue with your training to smash your time the following year
