Use this site and your VIN number to find out what came in your model
If you want to find out quickly look on the drivers door label for the Letter under "trans"
T would be a 4R55, 4 speed
D would be a 5R55, 5 speed
A '97 used an electronic VSS(vehicle speed sensor) but still has the gear on its tip.
Not sure if these can be changed like the cable speedo gears.
Google: speedometer correction gears
'94 and earlier were cable driven speedos
'95-'97 used the VSS with gear attached on trans
'98 and up used VSS without gear and could be on rear axle or trans.
The VSS speedometers can be calibrated by Ford Dealers
There are also add-on devices by Dakota Digital that can change VSS pulses for speedo calibration when axles and tires are changed, the SGI-5 Universal Signal Interface Unit will do that.