[Chas]

  There is a more to that speaker than just the field coil. It has the output transformer attached and built into the magnetic path for the voice coil is not only the field coil there is also a hum bucking coil. Direct substitution with a PM speaker and still have the radio power the amplifier section would require moving and remounting output transformer and adding additional filter condenser value to compensate for the hum reduction action of the hum bucking coil. That is if operation is desired. Alternatively simply replacing the speaker, leaving the radio OFF or disconnected and mount power and a switch for Blue-tooth.

Another method is to fully restore the radio. Get a blue-tooth to AM band transmitter and tune in the blue tooth station.

A third method is to locate and install an audio input that turns off the AM audio and enable a Blue tooth audio input to the amp. There will have to be some sort of impedance matching for the audio signal.

Since I am both a collector and restorer of my radios, my preference is the Blue-Tooth AM broadcaster. I have as yet to find one for myself though Advantage is any radio will work with it and no radio is modified...

Chas