Actually, there was a study out of Wisconsin back in the 90s (you young kids...). They used a bunch of recreational runners. I know, you're better than recreational...just listen.
They had 4 groups of participants - two "high" mileage groups and two "low" mileage groups. I think the high was ~50 and the low was ~30 mpw (which is too low imo). Anyway, one of the high and one of the low groups focused on getting in one long run a week, while the other groups ran basically all the same distance runs throughout the week. When it came time for the race (i think it was grandma's marathon or twin cities) the groups that performed best were the two groups that got in those long runs each week. Even the lower mileage group that did the long run ran better tha the higher mileage group that did no long run. Again, this was recreational runners (joggers I guess most would call them) who just wanted to complete a marathon.
Anyway, I'd say you should slowly increase your miles, no more than ~10-15% over what you were already running, though. So, if you were running 70, you could work your way up to ~80 mpw. You're still young, take those increases slowly right now. Your "primary" workouts should be your long run and longer tempos (which will NOT be at true threshold pace, but more like your goal pace for the marathon). Then every 10 days or so, get in some true tempo/threshold training - something like 4x10min with 2 min easy running between. I know a lot of people dont like the cookie cutter programs of books, but the training paces in Daniels running formula can REALLY help out with this. A lot of people i've met over the years (particularly younger guys) try to go too hard on threshold runs.
Of course...you have not mentioned how many weeks/months you have available for this. So, this could influence everything.