It's quite possible to use that flywheel as is for a PS/2 upgrade, just did one recently with a small flywheel. You just have to devise your own tach sensor bracket. I do them with styrene strips. I curve the first one and glue it to the motor, then cantilever them down to get the proper spacing for the tach sensor.
Here's a link to Custom Tach Tape Images that you can print any tach tape spacing you need to make the speeds work out with your flywheel.