Yes, as already established it is a Österreichische Saurer with a woodgas unit. All I need for the point, is the maker of the Holzgas unit. His name was written on this particular truck.
Guessed without success so far were the following makers:
Cabronia
Carbojura
Dietrich
Gustloff
Imbert
Klöckner-Deutz
Menck & Hambrock
Südgas
Wacker
Weda
Wisco
Zeuch