Does anybody know the composition of the 6th council and how the delegates were chosen?

Nyanatiloka and Nyanaponika were the only Western born monks to attend the 6th Council. I am curious to know the composition of the 6th council and how the delegates were chosen. Wikipedia says : > The council was attended by 2,500 monastics from eight Theravada Buddhist countries. Clearly there would have been more countries involved than the 8 Buddhist countries. Also the delegates from countries which were not predominantly Buddhist sponsored by a Buddhist country they lived in. Also how come Nanamoli Bhikkhu and Ven. Ñāṇavīra Thera did not make it as delegates?