Most of the vendors sell a new face plate decal that uses the kilometer per hour scale as mph.
Many people use a 5/8s speed reducer to get the speedometer to read 50 mph when it is pointing at what used to be 50 kph.
The problem is that the vss is now giving out the wrong speed to the ecm and the functions that are affected by the ecm are now screwed up. I guess a savvy chip guy could get around some or all of that in the chip.
The better way, imo, to do it is to have the speedometer recalibrated by a speedometer shop so that it read properly. This keeps the vss and speedometer in line so such things like tcc lockup are not affected.
At one time, Kirban used to put the new faces on speedometers and have them recalibrated. He would keep some on hand with various mileages and you would look for one with similar mileage to yours...I bought one and it has worked well for a long time.
It's a bit of a pain to change them out but not impossible by any means...
