I have the same setup and it’s the 17 tooth, white gear. I actually have an extra if you can't find it at your local dealer, but that is where I got mine.
A couple words of caution. First, I'm not sure if you are installing a new drive gear (on your TKO or not. If you are, then scratch what I said above because you need to switch to LH gears. If you are not, then you need to reverse your speedo. I got one from Tri State Motorsports. If your question was about the drive gear, then you need a 7 tooth, LH drive gear. Second, don't forget to order the clip along with the speedo gear. Third, you need gears for a manual and not an automatic. The Ford dealer parts computers don't make this distinction obvious as when I first went to get the part, I got a wine color 17 tooth gear which was wrong.
Try the ERA Manual for more info (p14 and p23)
ERA Manual and the Manual Update
Manual Update