Here's a couple of links to check out:
http://www.tciauto.com/tech_info/speedo_gears.htm
http://www.geocities.com/MotorCity/S...432/speedo.htm
http://www.lastgen.com/trannyinfo.htm
IIRC, the TH350 drive gear is held in by a clip an may be able to be changed out with the tranny in the car.
ST-10 owners will have a harder time since the steel drive gear is pressed to the shaft and the tailhousing can't be removed without dropping the reverse shaft thrust washers into the bottom of the case if they are not supported. Probably easier to pull the tranny if the drive gear has to be changed.
You might try pulling the driven gear and get a look at the colors of the drive and driven gears. Use the formulas above and on the web pages to see if you can match up a driven gear with the existing drive gear. It may not work, but it's worth a shot.
Dave
[This message has been edited by 455Dave (edited 10-30-2001).]