Ok here's my opinion:
Ok here's my opinion: possible, but too soon.
Here's why I think that: it's good that you've been running for a while, which is why I say "possible". You may be able to adjust your gait and strengthen your feet in time for that. However, I am about to do my first marathon barefoot, and have basically been redlining it injury-wise through the entire training plan, which has been 5 months long (you have 4 months to prepare for a September race).
Now a big difference is I haven't been running as long as you, so I'm not sure how much stronger your feet/ankles/etc. are than mine were when I started, but I can tell you from experience that you will reach a point where you will discover a weak link (mine has been my ankles), and 4 months will not be enough time to strengthen your weak link (whatever it might be) to the point where a marathon will be comfortable.
After 7 months BF/Min my ankles are comfortable through about 16-18 miles and then they get a bit stiff/sore, but not to the point where I can't keep running. The only reason I'm pushing past that is because it's an inaugural marathon (I reall want to be part o the 1st ever Kalamazoo marathon) and the local newspaper has been following my progress. I'll be bringing along some cushioned trainers as an emergency 'chute for the last few miles, but I won't use them unless I absolutely have to.
So long story short: based on my experience I would strongly suggest aiming for a half if you plan on doing it BF/VFF and then aim for a full in the spring.
Edit: just wanted to add that when I first signed up for the marathon I asked a similar question. Everyone suggested aiming for a half instead. I didn't follow that advice, which I freely admit wasn't the wise choice. Not that the experience hasn't been rewarding, but I know this was a dangerous decision on my part. So as one person in a hurry to another, please consider slowing down a bit.