MPH to KPH

Hi, I live in Perth Western Australia and my '79 KZ1300A1 is a US import and has an MPH speedo, I have sourced a new gauge plate in KPH and was wondering what (if anything) I have to do to the speedo drive to make it accurate, as the original speedo had KPH in smaller blue numbers.

The front wheel drives are the same. The "guts" for a MPH and a KPH look identical but they are not.  The gearing in the head itself is different, which allows for the various face plate increments.  I discovered this when I had to cannibalize 2 instrument clusters to create a new cluster on a recent '79 "Barn-Find" restoration. 
You would have to install a mechanical converter on the front wheel-drive
 
 

Another option would be to replace the speedo drive gearbox with a kilometer based gearbox. I see several gearboxes on EBay and one of them is located in Canada. It would be worth an inquiry to see if it came off a bike with a kilometer speedo head. My 1980 B2 is a Canadian bike with a speedo clocked in Kph with a 240 Kph max on the clock. I'm sure there are a few different drives out there because some of the bikes had 160 Mph gauges and some had 85 Mph gauges, Maybe have a read through this search   Using the search tab for "speedometers"