Knechtle et al 2007 performed an anthropometric analysis of 8 endurance athletes during the Deca Iron Triathlon. The DIT is a competition where athletes perform an Ironman Triathlon 3.86km swim, 180.25km bike and 42.2km run- every day for 10 consecutive days. This type of event goes far beyond standard endurance and will test the physical and mental limits of what even well-conditioned athletes are made of.
After looking at standard measures of age, height, weight, bmi, leg length, body fat % by skinfold, and resting heart rate- they found no direct correlation between their data and finish times. It is important to keep in mind this was a very small sample size (8 runners of 18 total, and only 11 finished the event).
Thus, at this time- for extreme endurance events, no specific body-type besides those of a general runner can be determined to help improve performance.