you lost me lol its factory AM/FM/Is it a stereo on the FM side? Rear speakers will help.
I think when FM started out there were very few stereo stations, they required more broadcasting power. In 60's most radios were FM only, don't think the circuitry was inside to separate left&right. This may turn out to be not much of an answer!Is it a stereo on the FM side? Rear speakers will help.