Announcement date and other minor issues
The article states in part:
"The first 350 C disk file became a commercially available product on September 4, 1956,"
Sept 4th is the date of the internal publication by IBM of Announcement Letter, 256-114, the public announcement was on Sept 13th . I suggest the latter date is more in keeping with the term "commercially available", see Computer History Musuem's IBM RAMAC 350 article for list of all dates.
I'm not sure wher the phrase "350 C disk file" comes from or is historically accurate, particularly the letter C. Nor is it clear that the term "305" was used externally for the RAMAC 350. The Sept 4th announcement letter refers to ""The heart of the system is the IBM 350 Random Access Memory ..." and the same term is used in the earliest 1956 and 1957 publications, see e.g. "The Random Access Memory Accounting Machine. The IBM archive refers to it as the IBM 350 disc storage unit.