Example of a simple sub 2:20 plan
14 Day Micro-cycle (90-110 miles per week)
5 Stress Workouts per Micro-Cycle
Day 1: AM 16 x 400m Hill PM 30 min jog
Day 2: AM 60 mins easy PM 30 mins easy
Day 3: AM 60 mins easy PM 30 mins easy
Day 4: AM Either 30 min or 60 min Tempo PM 30 min easy
Day 5: AM 60 mins easy PM 30 mins easy
Day 6: AM 60 mins easy PM 30 mins easy
Day 7: AM 120 mins fast finish (90/30) or steady state
Day 8: AM 60 mins easy PM 30 mins easy
Day 9: AM 60 mins easy PM 30 mins easy
Day 10: AM 6 x mile PM 30 mins easy
Day 11: AM 60 mins easy PM 30 mins easy
Day 12: AM 60 mins easy PM 30 mins easy
Day 13: AM 140-150 mins easy pace long run
Day 14: AM 30 mins easy PM 30 mins easy
On days 2, 5, 8, and 11 add in 8 x :20 strides in one run
Repeat micro-cycle 4-6 times (8-12 weeks) leading up to your marathon + 7-10 day taper.
Notes:
Day 1: 16 x 400 up a moderate hill (3-5% grade) at roughly 5-10k pace with jog down recovery
Day 4: Alternate micro-cycle between 30 min Tempo at 4-5% faster than MP (marathon pace) and 60 mins Tempo at 0-1% faster than MP
Day 7: Alternate micro-cycles between 120 mins with the first 90 mins easy and the last 30 mins at MP, and 120 minutes steady state of 5-7% slower than MP.
Day 10: 6 x 1 mile repeats with quarter mile jog recovery - repeats done at 8-10% faster than MP.
Day 13: 150 minutes at 15-20% slower than MP
Easy pace is usually 15-20% slower than MP, occasionally up to 25% slower if needed after a particularly tough workout.
There are plenty of variations to this and ways to enhance some of these workout depending on many variable, but this gives you all the basic building blocks needed to run a marathon very well in your situation (as described) if you are looking for a set repeatable schedule.