The 4-track came first, via Muntz. It was soon competed-with by the factory 8-track units. Many were add-ons to existing factory radios. The strangest, to me, was the mix of Mono AM and Stereo tape.
My uncle bought a new '67 Caprice with the 8-track option with the AM radio. Front two speakers were in the kick panels. Rear two speakers were in the rear package tray, as usual. Sounded great. Could image the music to the windshield, which I thought was really neat.
The old 4-track tape cases were partially clear, so you could see the tape work, I believe? 8-tracks had the tape continuously rubbing against itself as the part on the outside would return to the middle of the roll to go through the cycle repeatedly. Sometimes, the tape would not re-load correctly and then you'd see an 8-track with the innards sticking out of it, laying beside the side of the road.
Cassettes came in about model year '79. Big thing was "auto reverse" as when the tape came to an end, it would go the other direction and play another track.
The 8-tracks were at about 3 3/4 inches/second tape speed. Most normal reel-to-reel units were at 7.5 IPS. Ultimate frequency response depended upon tape speed. The 8-tracks had a good sound to them, as a result.
Cassettes were at 1 7/8 IPS tape speed. Which necessitated huge improvements in tape technology (iron particle size) in order to have decent sound quality at the lower speed. Cassettes, being smaller, were easier to store in a box under the seat (non-power seat, of course).
On the factory tape-equipped vehicles, the OEMs put a demo tape in the glove compartment to showcase the performance of the new tape sound system. In later years, other tapes were used to explain the operation of the main vehicular systems, so you didn't always need to read the owner's manual, at least just to know how to drive the car.
The noted cassette tape to 8-track adapter was an interesting work-around. But due to the tape speed differences and other electronic equalizations for the cassette to work well, sound quality with those adapters might have suffered a bit from a true cassette tape player. But it still gave you options!
I believe that in those earlier years, the 8-track units were also available in Factory Accessory Kits, from the OEMs. Until the instrument panels could be redesigned, even the factory-installed units were "add-ons". Finding one of those earlier 8-track kits, with instructions, and the demo tape might be interesting.
That Imperial looks very nice.
Enjoy!
CBODY67