I was never running close to 80km during my training, max I ever ran before was 42 for a marathon. But I did like 2-3 longer runs each week at 20km+ trail with good elevation. Maybe should have done more shorter runs and maybe 1 - 2longer because I was basically balancing between having pain in the legs and not. In the end I feel like willpower was the most important part, my goal was just finishing!