EUREKA!!!
Thanks a lot for the input/help/info you all have provided. With that and looking through old manuals and spares catalouges I´ve come to the conclusion that what I need is a RM400 (C,N or T, doesn´t matter) rear wheel axle and the chain adjusters to go. I could try the Maico item as well but I really think there shouldn´t be a problem finding a standard RM axle.
Again, THANKS!
regards Jens