Old British motorcycles, of which I own several, used Smiths spedo drives that came in Mile and metric flavors. Miles units resulted in 1000 revs per mile and metric were 1600 revs/mile. The standard for miles on US spedos is 1000 revs/mile. Speedo shops have or can get adapters that are used on trucks when axle ratios are changed. They come in many ratios. So there may be one for a metric conversion.
