I agree with Ryan — even down to thinking in the same terms (“different beast”).
On the other hand, I know a few recreational/fitness runners who have finished marathons who were less fit and less prepared than you are. Of course, they never aspired to be marathon champions and they probably spent much of their race socializing with the runners around them. So, I suppose that if you can truly accept success as finishing no matter how slow the time, then you can probably do it, but that doesn't necessarily mean it's a good idea.
Great job at Fox Cities. That must have been fun. Good luck with the thyroid issue.