Y'all are thinking too much about Over Kong Gun.
Kong Gun in Japanese = 猿王銃
which is literally translated as "Monkey King Gun".
King Kong Gun in Japanese = 大猿王銃
which is literally translated as "Great Monkey King Gun".
Over Kong Gun in Japanese = 覇猿王銃
which literally translates to "Supreme Monkey King Gun".
Once the panels come out, we can ascertain whether it is a regular Kong Gun or an inflated Kong Gun (basically KKG type attack) based on whether Luffy blows into his arm before executing the move or not. I'd bet on it being closer to a KKG than a KG though, if you ask me.