Speedometers are calibrated using magnetism. When you install a new drive, it has no magnetism in it. AutoInstuments 'zaps' it with a magnetizer, and the speedometer is then connected to the calibration machine. Autoinstruments then takes a demagnetizer and literally sucks the magnetism out of the drive a little at a time, until a correct calibration is achieved. If you go too far, you have to zap it again and start over
so just having a speedo shop recalibrate one's current speedo might be a good option for people doing a conversion. Especially if there was a "group buy" to have a bunch of speedos recalibrated to 14o mph all at the same time.