When radio bored the car owners of the 50's, they didn't have XM, Sirius, CD's or cassettes... they had record players!

http://ookworld.com/hiwayhifi.html has the most complete look at the press releases, magazine reviews, and sales brochures

You were limited solely to the releases made available by Columbia, and as you can see in the listings, these were somewhat limited. I'm no expert on what was available to them, but I'm guessing that many of these releases were remasters from Columbia's back-catalog. Note the complete absence of serious jazz, rhythm & blues, country and rock 'n' roll.

http://www.imperialclub.com/Repair/Accessories/HiWay/Chrysler.htm