There is an electrical plug at the tailshaft. Thats the speed sensor, or VSS. The speedo gear is at the end of that. The auto has another 'gear' on the output shaft (called a drive gear), which i believe is machined into the shaft itself. To change that you have to pull the trans and tear it apart. You can leave yours alone, just get a new speedo gear.
The 5spd has that same VSS connection. The output shaft has a gear that fits over the output shaft. Unlike the auto, that gear is removable (i think) without tearing the entire transmission apart, but it is easier to change with the transmission out of the car.
Following that link, youre transmissions has an 8-tooth drive gear and if using a 3.73 it calls for a black 23 tooth speedo gear. You may still need a speedcal to get an accurate reading tho.