Hey Orcas, glad to see you found another GJ. It looks really nice, on par with my silver and black one. I think I've got mine and its matching GJ mixte sold to a collector in CA

The short cage Jubilees were the lightest derailleurs on the market at that time. The addition of a long cage really didn't add much weight, so they're still incredibly light. The sexiest looking rear derailleurs of all time IMHO! As you have been told, they are a little fragile, so they take a bit of finesse to shift them ... don't be ham-fisted with them. You can only use up to a 28 tooth sprocket on the rear but with the long cage you can wrap up a lot of chain, so you can go really low on the front. The Stronglight 49d uses the same chainring pattern as the TA Cyclotourist, so you can get chainrings down to around 24 teet (maybe even smaller, I"m not sure). The Jubilee front derailleur handles a pretty wide range.

I'm building up a '75 Grand Record that I'm going to convert to 650B. It will use the long cage Jubilee, TA Cyclotourist 48-44-26 triple, MAFAC cantilevers and Lyotard Berthet platform pedals. Trying to keep it as much French as possible.

Enjoy your GJ!

Here's my matched pair:

And the raggedy Grand Record frame that will be my 650b conversion:

And the rest of the Moto collection ... a '72 GR (completely Campy), '72 Le Champion and a spare '75 GR frame and a "& GJ Mixte for my wife