MP3 CDs were definitely a thing, including ones people burned themselves, but I don't think I've seen anyone use a cassette adapter. Most people put aftermarket CD stereos into their cars.
American-designed cars often had nonstandard sizes for car audio even before fully integrated entertainment systems became common. My 2001 Chevrolet has an odd, not-quite-double-DIN-sized space. If I wanted a screen for it, I would have to do some physical modifications to the dash or buy one that has a smaller main unit and a screen that sticks out from the unit (to avoid other overhanging things near it). For now, I'm happy to keep using the Bluetooth unit I put in it fifteen years ago.
