Do a forum search for 'mph converter'. You wire it in and it changes the speedo calibration to mph. No need to touch the dials. You can get them off Ebay. It also moves the 180kph limiter to 180mph...
What will cost extra is if you want to convert the current odo reading into miles... However, if you just make a proper note of the reading when you added the converter, it'll be fine. The odo will count miles once the converter's on.