Copy and paste from the goggle.
The longest passenger car ever built not a limo or custom job, that I could find, was the 1975 Cadillac Fleetwood Seventy-Five.
It has a total length of 21 feet or 252”. General Motors manufactured it and was classed as a full-size luxury car. There were two versions: the Nine Passenger Sedan, and the Limousine, which had a glass divider.
So there you have the long and short of it, at least the long of it. Some of the longest cars of the era, with styling, grace, power, and comfort in spades. Those were the days.