Here are some early reports (so early it preceded the lean terms widespread use). It also means the focus hasn't already been set by the Machine that Changed the World but it is the same stuff that those that studied in 1980, 1990, 2000 or 2013 saw - it is more about respect for people and using everyone's brain than any specific tool. And these articles have a bit more focus on using statistics and data than much of lean literature today (partially because George Box and Dad were statisticians and partially, in my opinion, because current lean literature is light on using data).
continue reading: Early "Lean" Thinking