My hat is off to you Pal!!!
This type of vehicle is my primary field of research and I spent maybe 4 hours trying to solve the puzzle without result.
In the end, after you gave us the coach builder's name, it seems the only photo on the internet is the same as the quiz photo and is only a small one connected to the history of Speckbacher and that gave no details. In fact, there are only perhaps 3 photos of their work on Google/Austria.
Good job my friend!!
Bill
