You're very welcome Stefan!
I was talking to Chris Shepherd about these stiffeners. Chris is building a magnificent replica of a D.Va here in Australia. He is a member here, so if he sees this thread we might be able to ask him to post some photos of this area if you're interested. I saw his Albatros when he had covered one side only, and if I am not mistaken, the port side had the stiffeners attached and exposed. I was very surprised to hear Chris tell me that the stiffeners were not even checked into the longerons and formers, as I would have expected them to have been. He said that he had photographic evidence of this. It's a perfect example illustrating the fact that in some respects these aeroplanes were works of art, and in other respects they were quite roughly constructed.
Regards,
David.