As far as being able to do it your self, that depends on your abilitys. The driven gear that is the one in the housing that the speedo cable screws onto, it is easy, just remove the bolt that holds the housing into the trans, the drive gear, that is the one that is on the output shaft of the trans, you will need to remove the driveshaft and tailshaft of the trans to get to it. Also depending on the trans you have, the gears are different, and on the TH-400 there are different speedo gear housings for the different range of gear teeth count. Here is another source to determine the gears you need for the speedo, it is from a Nova Site that I am on also, but will work for GM cars.
