speedo gauge I am guessing the numbers will not be in the same spots. For it too work properly 120kph would have to be in the exact same spot as 75mph on a USD cluster. The faster you go the larger the discrepancy will be.
If you are dead-set on having kph you could probably swap in an entire jdm cluster but this may cause other problems, I do not think there is any difference at the speed sensor.