I've done pretty much exactly that. It wasn't pretty. It's very hard to hold yourself back enough, because marathon pace feels so much slower than all of the other quality work. I was hurting pretty bad at 16 miles, and by 20 it was a joke. I was running like 7:45s.
The real problem is that my long runs were just 14-18 miles, and at a pretty easy pace. If I pushed the pace on my long runs, I'd never have been recovered for the kinds of track workouts I was doing.
Now, if you have enough time after your track season, and you're not totally fried from too much intensity, then you should be able to do a 6 week race specific cycle and pull off a decent marathon. You should be aerobically very strong. The main thing is getting in lots of long miles at MP. Also, a small cut in mileage will facilitate more recovery so that you can jam a little more quality into such a short time frame.