ACZR

Hi everyone. I have searched and read and read and searched and while there is quite a few topics on this no one seems to have had quite the same situation as I have. So, I believe I have discovered why my speedometer will not work and am now looking for some info from the experts to make sure I'm on the right track. So I have a 1998 Tacoma with a manual transmission and the 3.4. The transfer case gave up the ghost so I swapped in one from a 2000 4Runner with the automatic and the 3.4. The speedometer hook up between the two is different due the the transmissions. The standard needs to take it from the back of the transfer case. To me the worm gears in transfer cases look the very same. If I put the truck in neutral and roll in back and forth I can feel the worm in the transfer case spinning, so I know that is good. I then taped a drill to the speedometer gear and had some one watch the speedo inside the truck, it got up to speed no problem, so that is working fin as well. So though process of elimination I have concluded that the speedo gear is too small and there for is not meshing with the worm. Does this sound like a probable diagnosis? I have called Toyota and the parts guy told me that all speedometer gears are the same diameter regardless of the tooth count, which seems impossible from what I know about gears. So now is the second question, what is the best way to find out which gear I require? Is there a chart somewhere or is it just a matter or trying gears until I find one that fits? Thank you for any I for you might have!!