Fuselage AM to AM/FM swap

I have a '73 Plymouth Fury that came out the factory with an AM radio. My goal is to find a factory AM/FM radio, hook that up and just replace the original speakers and use an FM transmitter connected to my phone. I'm wondering if the speaker configuration is different in a car with FM radio compared to an AM radio optioned car? In other words, does the dash have two speakers for stereo? I haven't taken it apart to check yet but I'm questioning if I'll need to make any modifications to the...

Fuselage AM to AM/FM swap