He should have shown at least one photo of the Stallard dropout, which was adopted by a few other builders as well IIRC (someone here will know the deets there).
Stallard's own drawing showing the "gear ends":
Why choose between verticals and horizontals, when you can have both?
The long lower tang was there to prevent the wheel from going forward enough to foul the derailer (Osgear and similar styles) during a wheel change.
Mark B