Overseer and Elder convey the meaning just fine. No need to import new words if the language already has them. "God", "Heaven", and "Hell" are AngloSaxon -- the church had no problems appropriateing those words.
Overseer and Elder do nothing of the sort, especially Elder. Since when did people become "elders" in the normal sense of the word through the laying on of hands (Acts 13.28, 1 Timothy 4.14, etc.)? How does "overseer" imply a power to rule the people of God (Acts 20.28)?
The Church used God, Heaven, and Hell beause they already conveyed the necessary meaning in Anglo-Saxon pagan religion. But she also adopted Theology, not Godology, Soteriology, not Heavenology, etc.