Interesting point Nathan.
Indeed, "Modernism" evolved out of many changes & movements throughout the 19th century & "machines" & their design played a great role in it. After WWI, fascinated by aviation & aerodynamics, designers pushed car design into the modern era, ultimately breaking into mass produced vehicules, like the 1938 Porsche designed Beetle.
As for what is MCM? Automobile design underwent a major change after WWII. Its evolution, which had been very similar on both sides of the Atlantic until then, rapidly diverged into distinct schools.
And in many cases, the very designers involved in this "split", were people who had fled Europe during the war to seek refuge in the USA.
So where could we "situate" the "starting point" of MCM car design? Postwar USA: ~1945, same as in architecture...
Where could it "end" is indeed an interesting question.
The cultural revolution in the second half of the 60s I'd say is a good benchmark.
The 60s brought much criticism onto the modern movement & the wish to start on a clean slate. You could make a parrallel here & see the work of the Italian firm Superstudio at the end of the 60s.
As for how this translates into car design? My impression is that something "new" emerged from Europe at that time, while american car design lingered on (still?), "lost" in its past glory, until enough time had gone by to move into "retromodern"...
NOW! This being said, the Coronet had a predecessor in it's 1959 form:
Similar "eyes" on the 1959 Bonneville:
On the subject of peculiar "eyes", the Batmobile's (1955 Lincoln Futura Concept Car) were used on the 1956 Lincoln Premiere:
...and back to the Coronet
1935 Tatra T77-a