All 1955 and 1956 Ford products with an automatic transmission would start only in neutral. I am not sure about the years prior to 1955 but would suspect they were the same. I know starts in park could be done by 1962 but not sure about 1957-1961. Probably changed when the fordomatic transmission was replaced with the cruiseamatic, which I think was first available in 1958.
Why the fordomatic was designed to start only in neutral is something I have never thought about until now.