As I got it right I guess the next time I'm around in your part of the woods I can come along to play with it...
I did not know about the data back. But in the photo of the film chamber one can see a patch inserted into the body, covering part of the image area.
I assume the data exposing was done via transparencies (dials etc.) and not by LED matrix. Have you got any information on this?
EDIT: I was right, data exposing was via flash, thus no matrix.
But still I do not know whether by readymade dials etc, or by handwritten inserts.
So, you know what to look for next.
(Luckily I'm not a collector...)