Philia_Bear;121882 wrote The gears and cable are the same for both mph and kph so it's just the gauge itself that is different
The MPH one I have here out of a 73 164 is marked W 0.990.
Metric ones? There's also an r 0.605 from a Canadian 240 IIRC, and also used in the 242GT, plus a metric W 0.640 from a 74 142 here too.
The GT MPH speedo is a 0.990 ratio according to the parts book (Group 3 page 96) and the GT metric one is a 0.617 according to the same source. This info fits with the OE 164 speedo I have being marked W.0.990. So if
@ab1 doesn't have a 0.617 marking on his OE speedo, I'm willing to bet it's not from a 164, and that may explain the dodgy readings.