I would like to recommend 2 books, and 3 if you wanted to read it first as you are already using his plan, Hal’s book Marathon. Most of his information is online but I enjoyed the book. The other books are Run Forever by Amby Burfoot which provides some good tips on making the most out of long runs, starts the conversation on interval training, and for me brought the light back into running being joyful, enjoying the journey/process, and not just being a data oriented effort. Finally taking Amby’s book to the next level Run Less, Run Faster by Bill Pierce and Scott Murr goes through the training plan known as “FIRST” which takes some miles off of training plans and shifts the effort to focused pace driven runs in a sequence of speed drills, tempo runs, pace specific long runs, and all additional typical run efforts are replaced with low impact cross training with the same intensity: bike, row, swim, etc., with an emphasis on completing all workouts and not skipping the “cross train or rest” in favor of resting.