Speedometer doesn't work..

The 1996-1998 model years use a VSS transmission sensor. The 1999+ uses an OSS sensor. The electrical output of the two sensors are NOT compatible with each other. The sensor type used has to match the PCM and the wiring harness.

The VSS sensor is driven via a worm gear. The OSS sensor uses a reluctor wheel (like ABS tone rings). To further complicate things, in 2004, Ford changed the number of teeth used on the OSS reluctor wheels. Ford's intent was to standardize across the product line.

So you see that the model year of the donor car is important.

Your 1997 came with a VSS sensor. A transmission from a later MY will have a OSS sensor. For more information about the differences between VSS and OSS, check out:

T-45 Tail Shaft Swap - Ford Mustang Forums

An extended range SpeedCal can convert an OSS sensor signal to what a VSS style car is expecting.