Totally winged it when I ran 2:38.. next marathon after that got cocky because I had trained and blew up hard and finished at 2:45
I remember doing a 22 miler averaged at 6:40, an 18 miler averaged at 6:30, and a good 15 miler. lots of 11-13 mile runs though. Think I only really did one workout which was something like a hilly 6 mile way too hard tempo at 5:35 pace. My plan was to run the marathon with a family member at 3:45 pace but found out a friend was doing it and he talked me into actually racing.
Biggest thing was the race group, was tucked in with 10-12 people in the 2:40 group, but as they say ignorance is bliss- remember clicking through at 6:30 the first mile, my friend who I got separated with at the start found me around there and said "eff it I'm bored let's go" and we started dropping 5:50's until we caught a group of guys at around 4 miles and there was lots of open space in front of them and we decided to calm it down, they were metronoming 6:0X's and just tucked right in.
I had run a hilly 75:40 half marathon a few months earlier, and a 15:50 5k on an indoor track. 8k XC from fall before was low 27, for comparable times. I think biggest thing for me was this was the first time I had consistently been hitting 60+ mile weeks, but more so started doing "real" long runs, had usually always capped at 13 before.
When I was actually training for the marathons I blew up in I remember feeling super fit after having a decent amount of 18-20 milers, 10-13 mile MP tempos, 10+ reps of 2 min on 2 min off fartleks, cruise miles, and 2 x 4 miles at HMP. I don't really remember doing any 2 mile repeats but have heard from many that that is key.