Mine was destined for France in 2000 and it has been converted (by the importer) to read Miles instead of Kilometers.
It was done with a little electronic module that sits in the connection box under the tank and has the speedo sender wire cut and soldered to each end with 2 wires to the +12V and earth wires. The module (I suppose) simply outputs 5 pulses for every 8 that it receives.
It has a "MPH" sticker crudely placed over the "KPH" on the dial. - It works fine except that you can't really tell the difference between 30MPH and 35MPH cos the resolution is poor at low speeds.
Oh, and the speedo reads up to 240MPH ....
I tried to google for a similar module but it failed to find anything. You might get lucky if you persevere.