Dear Paul,

p> What is the the Pali name of the book that contains the
p> Dhammapada stories?

Dhammapada.t.thakathaa .

p> In A Handbook of Paali Literature, Oskar Von Hinüber refers
p> to the Dhammapada.t.thakathaa and attributes it to Thera
p> Kumaarakassapa, an otherwise unknown person who translated
p> the work into Pali from the Sinhalese.

What are his arguments?

Wilhelm Geiger atributes this commentary to Buddhaghosa.
Moreover, in the end of the text there is his name.

Best wishes,
Dimitry