Thorsten,
That is a very interesting looking speedo indeed! I've converted my share of speedos to metric scales and Odometers, but have not yet run across one like that. I recently saw a picture of a 67 Shelby (original export car) which had a 220 km/h speedo done in the same fashion.
Where are you located? If you're willing, I'd gladly take a closer look at the speedo and also check its calibration. I'm almost willing to bet that it is an original unit and has not been "re-printed". The 67 Shelby which was done in the same fashion would support that theory but an up close and personal inspection would confirm.
Regards, J