There's 2 ECU's listed for the 97Q:
Fed 23710-6P100
CA 23710-6P600
You'll want to match ECU's. From what I recall reading, if you install a CA ECU in a FED emissions car you'll have an eternal EGR code that won't clear. Removal is very simple. Pull back the carpet square at the fwd corner of the passenger side kick panel and remove the 10mm nut. I'm not familiar with the 97Q but you may have to pull off the lower glovebox panel to pull off the kick panel. To get the ECU out remove the connector first before removing the screws holding the ECU to the chassis. There's no room to pull it out if it's still connected.
Before you rerplace the ECU....It is a faulty speed sensor that makes the tach and other cluster functions (speedometer?) operate. If it were me I'd do the speed sensor self-diagnosis sitting in the front seat in the comfort of my garage before I replaced the ECU of a car whose engine is running well. See the AT section (Page AT-23) of your FSM for the self-diagnosis procedure.
http://www.nicoclub.com/FSM/Q45/1997_Q4 ... Q45/at.pdf