BelowAverage: It can be done. I could not have done it as I did not have your talent (2:50 marathoner) I did have an incredibly busy schedule so I was limited and kept my miles in the 70-75 range while only running singles. You cannot discount the high number of individual runs of 10+ miles - builds strength and the marathon is a strength race.
Due to your schedule and the lower mileage for your goal, I feel your best bet is to run singles. Here is how I would do it: I would break the training down into an "A Week" and a "B Week"
Easy = run how you feel that day (6:30-7:45)
A Week
Mon: 8 miles easy
Tues: 12 miles easy with 8 20 sec. strides at the end of the run
Wed: 2 warm up, 6 @ tempo pace, 2 cool down
Thur: 12 miles easy with 8 20 sec. strides at the end of the run
Fri: 2 warm up, 4X1600M @ 5K pace with a 4-5 min. rec., 2 cool down (track)
Sat: 6 very easy
Sun: Long Run (eventually this should be in the 20-24 mile range, I would get at least 8 long runs in)
78-82 Miles
B Week
Mon: Off or and easy 6 mile shake out
Tues: 12 miles easy with 8 20 sec. strides at the end of the run
Wed: 12 miles easy
Thur: 2 warm up, 8X1K at slightly slower than 5K pace (3 min. recovery) 2 cool down (track)
Fri: 12 miles easy
Sat: 6 very easy
Sun: Marathon Pace Run: 2 easy, 8-13 @ 5:20 (eventually work up to 13 but I would do at least 5 of these at 11+ miles) 2 cool down
67-74 miles
Good luck!!