So am I. I didn't know Zenith had quad sound in any of its large three-way consoles of the '70s; however, if the feature was in any of their sets, it likely only lasted one or two model years. The reason is that quadraphonic stereo never really caught on with audiophiles; in fact, the system was an utter failure (too many standards for and too much bickering over Dolby, quad FM broadcasting and so on) and quietly disappeared by the end of the decade. (I have seen only one quad system in my life; that was 31 years ago.) I remember reading an article on quad sound in an old issue of an electronics magazine in the early 70s which began: "Four channel sound. It's FANTASTIC! It's STUPENDOUS! It's COLOSSAL! And it is also A BOMB!"
The author of that article had the last part absolutely correct. I don't think quad FM broadcasting, for example, ever caught on in many if not most major cities except New York, Chicago and Los Angeles. (The networks may have tried quadraphonic-stereo broadcast experiments on their owned stations in those cities.) When I was a kid growing up in suburban Cleveland in the '70s, I don't remember hearing any four-channel records or tapes, much less reading about or hearing any of the city's FM stations broadcasting in four-channel, although the classical-music station might have tried its hand at quad for a few months.