The main source seems to be "Kishi and Corruption: An Anatomy of the 1955 System", Samuels 2001: https://www.gwern.net/docs/japanese/2001-12-samuels-kishiandcor

The main source seems to be "Kishi and Corruption: An Anatomy of the 1955 System", Samuels 2001: https://www.gwern.net/docs/japanese/2001-12-samuels-kishiandcorruptionananatomyofthe1955system.html https://www.gwern.net/docs/japanese/2001-12-samuels-kishiand... "Kuromaku and the Underworld" section. (Aside from the lack of proper citation, tracking down a copy proved fairly challenging, so I have to wonder if OP has actually read it.)