The field coil usually also acts as a choke in a pi filter in the power supply. If you use a PM speaker you should replace the field coil in the circuit, assuming you no longer have it, with an appropriately rated choke. It should have about the correct resistance also. You can add a series resistor if necessary.
What the model number of your Westinghouse? There's probably a schematic for it on
http://www.nostalgiaair.org
John Y.