Well, I'm not an expert on ancient genres of literature, but it seems to me that Job and Jonah portray themselves as non-fiction just as much as any other novel does today. I don't think there are many works of historical fiction that explicitly say that they aren't non-fiction, for instance, a person just knows. Similarly, I think a person in the ancient world might be aware that Jonah was fiction, if it was, without it having to be either implicitly or explicitly stated within the work.

As you mention, genre is being taken into account more, and that is where my stance comes from. I think it's incorrect to project a modern way of writing history, for instance, on ancient writings, where their intent was not as much about relating the facts entirely accurately as it was interpreting the events.

I could drone on and on about why I think as I do, but this isn't the "convince all the non-Catholics to adopt my beliefs" thread. :)