I am very grateful to Christophe Vielle, Deepak Bhattacharya and James Hagerty for their nearly instantaneous reply to my query. I know now where to search for the "body-churning ritual" antecedents.
James Hagerty's monograph is, happily, on hand. But, the University of Warsaw Library informs me that the 1943 Georges Dumezil's book is not available in Poland, and - that the University's JSTOR does not possess in its resources either of the journals (Journal of the Bihar Research Society, Studies in Religion) you mentioned.
Will try to get access to the journals via my ex-students (one lives in India, the other in England).
A question to Prof. Bhattacharya: any detailed information on U.N. Ghoshal's work re "Vena's oppression"?
Best,
Artur Karp