Robert, the guard looks just like the ones on a couple of Robust I have, check this one out, a No7, made 1925-30 I think;
http://s36.photobucket.com/albums/e40/james-l/Robust/

Some where around I have the swivels, I seem to remember a German gun I owned once with this step, a Nimrod I think, it had several other locking gadgets on it. Nothing is really new with double guns, most thing have been tried before I think.

Jim

I learn something every day, and a lot of times it's that what I learned the day before was wrong