I have the metric
speedo put back together with a working odometer in it. I was able to take the odometer apart by pulling the thick brass washer off the shaft. I heated the pliers with a soldering iron and held it on the washer for about 20 seconds and then twisted it off.

In comparing the standard odometer to my metric one I found some notable differences. The drive gear on the standard odometer has fewer teeth ; 20 as opposed to 25 on the metric odometer.

Another difference is in the direction the odometer turns. They turn in opposite directions, as seen by comparing the way the numbers are placed on the wheels; on the left is a metric one; the rest are standard.

Another difference is the worm gears that run the odometer. First, metrics turn the opposite direction, as seen in the last picture, so the first gear is cut to turn "backwards." It is also metal rather than nylon like the standard ones. This means that it can't act as a fail-safe to keep the odometer from internal damage in case of a jam up, as Doug7740 mentioned earlier.

This resulted in damage to the tenths numbers. The 2 teeth were stripped off of the inside of it.

For comparison:

So I got the odometer back together using all the old metric numbers except for the tenths, which is from the standard odometer. This means that all the numbers will work correctly except the tenths, which will appear to be counting backwards... Best I could do. I have my doubts that this fix will last for the long term. I also wonder if any of the metric speedometers lasted very long. It seems that the odometer would turn about 1.6 times as fast, and the worm gears would have to turn even faster, as the metric driven gear has more teeth. On the other hand, there probably aren't very many of these out there!

I don't know if this info will be useful to anyone, but I found it interesting (like a bag of snakes)!