Only thing worse than trying to run a marathon on no training is trying to run a marathon on half-@$$ed training.
Speaking from personal experience: I felt like I had enough base training from a couple of years worth of solid running and 5K racing. Put in 35-45mpw on a very consistent basis. Ran three (hilly) long runs in the last month prior to the marathon, got sick over the winter holiday three weeks beforehand, and toed the line (Carlsbad Marathon) feeling a little too confident in my ability to BQ. Ran well (3:05 pace) until 17mi, when my mind got completely screwed by a archway of balloons at the top of the last hill on the course (figured that was the turnaround to head back up the highway toward the finish). Lost my focus, started cramping, shut it down at 19. Hurt like hell trying to start back up again until 22. Ran from 22 to 26, when I cramped again. Jogged the last .23 in. Depressed as hell for three days, which took a long talk from a friend to get me out from under...Coach (competed in 25 marathons) told me when I came back home I was a fool to run a marathon (in essence) on NO TRAINING. It took a year to *completely* recover from the damage I did.
Law of transfer does not apply. Bicycling is only good to train for bicycling. To run well you need to run.
My point is not to slam you. My advice: Have fun. Start slow, then taper off. Good luck. I think you'll have a bushel basket of hurt when it's all over. Hope you will learn to respect the distance like I did (Had Chinese symbol for 'respect' tattooed on R shoulder to remind me of experience.).