Thank you very much, Steven, Stevan and Chuck.
Luckily I´ve got that four speed block, I now say. The bike came with a three (which was no good at all and took a quarter of an hour´s worth of chiselling to be removed (How can anyone be so daft and fit a freewheel with the notches gone?)), that´s why I assumed it needed one.
Regards, Toni Theilmeier, Belm, Germany.