Jim, I don't remember the source but it was mentioned in more than one place that I read that the props did provide some fin like stabilizing effect and that the major reason for the small fins was the lack of props on the jet model. Certainly the size of the jet version fins was much larger than the prop shaft fairings.

Either way props do have a vertical fin effect and where they go makes a difference on what size fin area is needed.

And the name of the flying wing model with no fin? The Klingberg wing.