I took the non working factory radio out of my 54 Meteor ( Canadian Ford model, with a Mercury dash) and had it repaired by a local antique radio repair guy. My car is the original 6 volt positive ground and he was able to add FM to the factory radio. To use the FM, you just turn on the radio, and it will be in AM. Quickly turn it OFF and ON again, it will be in FM mode. To switch back to AM, just turn it off and on again. If your car sits overnight, or for days/weeks, it will stay in whatever mode it was in before.
Once I got the radio installed, I was thrilled with how well it worked. Next, I bought a 6 volt to 12 volt converter on Amazon, and installed a 12 volt power port in the ashtray. Then I bought a 12 volt Bluetooth to FM transmitter and also installed it in the ashtray. I now connect my phone to the Bluetooth transmitter, and tune in the radio to my PHONE! It's fantastic!! I use spotify and also have some music stored on my phone. I can even take phone calls while I'm driving, the transmitter has a microphone in it. It's not the best for phone calls, but for music it's great. It gives my music that old school AM sound through the mono speaker. People are really shocked that I can close the ashtray, and everything looks stock.
There are several radio repair guys in both Canada and the US, most of them will be able to fix up your radio to play FM music.
Someday I'll make a video of how I did this, the radio repair/conversion cost a few bucks (around 600) but I wouldn't trade it for anything.