If I was setting up the new sensor bracket, sensor and setting the air gap, the approach I would take would be to set the initial gap at 10 thou" and then shim the sensor away from the tone ring in 5 thou" increments until the reading from the sensor is stable. If the gap opens too far it will lose the signal obviously.
Probably around 20-30 thou" would work well, but just test it as you go.
Looks like you are going drag racing? Why bother with the ABS system at all??