Here "heads" is a metaphor for the more important people—the leaders of the clans. AT: "leaders of the clans" (See: [[rc://en/ta/man/translate/figs-metaphor]])
# These divisions were eight in number, corresponding to their clans
"There were 8 divisions based on the clans of Ithamar's descendants"
# They divided them impartially by lot
They divided them by lot so that the divisions would be fair"