world class 100km runners

You could start by taking a peak through The Lore of Running. Dr. Noakes, the author, spends a good amount of time discussing the Ultra crowd, especially Fordyce.

A few keys for making the conversion from shorter races to mid-length Ultras (i.e 50m or 100k):

1) continue incorporating some speed work in your program. While having speed itself isn't necessarily important in races of this length, the improved efficiency that comes with doing speed work pays large dividends.

2) Fueling is largely an individual thing for runners, so plan to do a considerable amount of experimenting on what works well for you. I suggest keeping a log of your experiments so its easier to track and learn. Educate yourself on the subject but also trust your insticts (and cravings). Your body will guide you.

3) No need to go exceptionally long on every long run, but rather find a pattern that works for you. Many successful ultra runners have found that going extra long once out of every 3 long runs works well for them, with the other two being more typical marathon training type runs with steady state or MP sections incorporated.

Hope you find this helpful and best of luck.

Thanks for posting. Totally agree with your point on efficiency. I'd guess the best speedwork for developing it is that which most intensely focusses the mind on good running form during the workout, which is likely another largely individaul thing.

Noakes does discuss Fordyce, but not his specific speed workouts, or the specific speed work element of other sub 6:40 performers buildup.

All sub 6:40 guys were pioneers: Each must have 'training experiments' that didn't work, as well as their great breakthroughs that did (eg Fordyce's long taper). It would be great to bring this info together in one place, discuss it, and save others from making those same mistakes!