Can you not change the speedo drive gears in the transmission like you can with American cars?

If not, you can also get custom-cut external gearboxes that go inline with the cable. I have one on my '57 Chevy and had one on my motorhome.



http://www.gaugeguys.com/

http://www.speedometershop.com/ratio.html

http://www.speedograph-richfield.com/html/minature_gearbox.html