The ideal way to select the cores is to measure the EMI field intensity to determine the peak
common mode current. Fluke may have a scopemeter that may be useful. In the absence of a
field intensity value, provide the following:

Motor volts, HP, motor full load amps, motor load peak amps if different than full load amps.
Diameter of the motor cable if all conductors are in one cable.
Diameters of each motor cable if the cables are separate and are not bundled in one cable.

Specifications on the cores may be found here:
Magnetec Common Mode Chokes