That's the type of machine on the top of my wish list. I have an eye out for an early cast iron zigzagger in general, so not entirely model or brands specific, but available bobbin type and 15x1 needle would be nice. The check spring needs a bit of investigation, a bit of a tricky one. Do you have any idea of it's age? I once came a cross some info on the first domestic zigzagger, possibly at least. It was a Munldos Victoria and if I remember correctly; introduced in the 1920s. It became very popular, and by the 1930s a few other brands had developed theirs.