Connect roue libre to rear wheels?

Hello to all. I am rather new in a group. I am restoring Rosalie 15 familiale. 
My problem is that when I bought her she had wrong gearbox. I found proper one (thanks to the club) but I don’t know what am I missing to connect it to the transmission shaft. Apparently 15 have small shaft between. I am posting photos as well. If anyone has some photos or solution I would appreciate. Thanks, Andrej