This is a fascinating derailleur. I got it from Brazil, and have been assured that it was made in Brazil, but who knows?
It shares a lot of features with a late 1950s/early 1960s Gian Robert model. It shares even more with a derailleur branded 'Super Gambato Padua' that is shown on Velobase. In particular it shares the slotted bolts and the pulley cage with the guide pulley concentric with the p-pivot. Velobase considers this 'Super Gambato Padua' derailleur to be manufactured by Gambato in Argentina. I believe that it was, in fact, manufactured in Padua in Italy, by a company the was started by Marcello Gambato that became Gian Robert.
Just to complicate the picture Gian Robert also had a manufacturing unit in Argentina.
However, both Gambato and Gian Robert derailleurs are heavily branded, and the early models are rather well finished and lavishly chromed. In contrast, my 'Brazilian' derailleur is clean of any branding at all, is crudely finished and is plated with notably nasty and flaky chrome. However, my 'Brazilian' model was not a cheap derailleur to produce, with castings used for the parallelogram arms and knuckles.
The hanger plate of this example has been welded and filed in some inexplicable way.
All very mysterious.