> They literally discontinued all other product lines
Not quite, as I mention elsewhere they continued incompatible low end systems, most prominently the existing business 1401 series, and used 360 technology to make the affordable 1965 1130. I would assume the same for the 1969 System 3, which eventually evolved in the AS/400 or IBM I as they call it now, which internally is still by far the most sophisticated mass manufactured computer system architecture.