One immediate question is the”Motor Sensor Board” - what is that for? Is it a tach for the sound, or for speed control? Both? What is it?
Yes, that is so the main motor maintains the commanded RPM- AKA Cruise, AKA Odyssey.
In some cases, that secondary function might also send speed relevant info for sound, but primary function is related to motor control since it is connected to the main board.
That said, this is what separates the amateur from the pros, IMO, when talking about upgrades and why legacy upgrades are not super common, not something "everyone" does. Basically, in a nutshell, you need a chassis and motor arrangement such that you can install this sensor and use a Lionel flywheel, encoder ring, and mounted circuit board and sensor.
May require pressing flywheels off, not damaging the motor, soldering on new sensor board, mounting the new flywheel and encoder.