Looks like you won't be able to just change the face, you'll probably need the electronics to go with it. The USDM & JDM speeds don't conincide with the same locations on the gauge itself.
Take the following positions for example:
9 o'clock = 45mph (72kph) on USDM vs 60kph on CDM
12 o'clock = 110mph (177kph) on USDM vs 160kph on CDM
3 o'clock = 175 mph (281kph) on USDM vs 255kph on CDM
So if you just swapped the faces, your speedo would be considerably off..
I wonder if that can be adjusted though to be at least within a standard amount of tolerance. I'm going to experiment with this . From face value the MPH dial looks pretty close to KPH. It's probably more a incremental linearity issue.