When cleaning my speedometer I discovered that what I thought was a metric Smiths unit was actually just a printed piece of paper glued to the face! So, I scanned it in and cleaned up the image a little in case it's useful to anyone else. If in some areas you require a metric speedo for importation, licencing etc, just print this out, cut it out and stick it to the face. It may take some playing with print settings to get it to print at the right scale.
Here's how it looks installed:
Thanks to Chris Williams for the updated overlay.