Speedometer?

Yes about the screws of the brake discs front left and sensor

there are no magnets at the disc.

The sensor use the magnetic field of the brake disc screws.

You can use the RC8 sensor but the sensor need the correct distance to the screws.

I do not have it in my mind but if the distance is not more than (let´s say) 1,5 to 2,0 mm you should be safe.

BTW: your project is fucking awesome - we want to see more when you finished this project