Looks like Helbig. The crossguards look thicker and made of cast iron. Why it doesn't have a makers mark?? Strange, since it's not an early ground Röhm. I don't think everything's OK with that piece, wouldn't go for it if I were you.
Another thing that caught my attention is that you mention that the fittings are cast iron, never had heard that could make iron fittings at the time, is this so?
