You really don't. Huret made a "knock-off". I have one. It shifts horribly compared to the Campagnolo Gran Sport I have in its place. The coil spring is not smooth in any way. Cool looking but functioally sketchy.
Hey Iab, never judge the original with a knock-off. I think Hilary knows what's going on. And Clydesdale Scot, based on the link you sent, the chain routing on the velobase.com site is definitely wrong according to the links you sent me. All very fascinating to me.
Velognome, beautiful derailleur. thanks for sharing that.