The black Competitions I have worked on when new while having Huret Jubilee mechanisms, were of the type for the Campagnolo form factor dropout. The Huret rear mechanisms were made in at least two ways, so this is where one has to be careful. Basically the upper body was machined differently for each and if I remember correctly the fastener was different as well.
We got one shipment at the shop for which I worked that were a "no go" for Campagnolo style ends, there was an adapter that someone made, but it then kept one to a 5 block as it spaced the mechanism further from centerline.
John Jorgensen
Palos Verdes Ca USA