Ok, it took some digging, but I think I found the history of FM car radios. In 1952 Blaupunkt made an FM only in-dash tube radio in Europe. This radio was later offered as a factory option by Porsche. In 1953 Becker began making AM/FM in-dash tube radios for Mercedes-Benz.

In the US, in late 1957 Lincoln offered an "FM Tuner Option" for its 1958 cars. This was a Bendix built all tube, floor mounted tuner. It also had foot controls.

In 1959 Motorola came out with the aftermarket FM900 tuner that was a hybrid and was all under-dash. It used the AM radio's amp. In their annual report, Motorola claimed they were, "the first major American company to mass produce an FM car radio." Apparently they didn't think Bendix was a major American company.

In late 1962, for the '63 model year, both GM and Ford offered all transistor in-dash mono AM/FM radios. GM's Delcos were available in full size cars and Corvettes, and Cadillac offered an add on multiplex unit. Ford's was Bendix built and available in full size cars and Thunderbirds.

Chrysler offered the Delco radios in their '64 Chryslers and Imperials. Dodge and Plymouth did get them until '65.

So, as Paul Harvey used to say... now you know the rest of the story!