The SX410 is not all metal. It has plastic arms hidden by thin sheet metal covers. I have no experience with the SX410, but I know it was used on some high end Peugeots. The model that replaced it is the SX610. It has the same hidden plastic arms and a drop parallelogram design. I like that one so much that I bought three of them. They shift at least as well as my Super LJ 6500. Broken pulleys is not an issue with my Simplex derailers because I've replaced them with Bullseye pulleys.

All I can say about the Huret is that it may not fit your hanger if it doesn't have the right adapter. It's a tabbed washer and there were three different types for Huret, Campagnolo and Simplex hangers.