Does anyone know the size/thread for the bung that does in the coolant gallery behind the exhaust toward the rear of the engine?

I just filled up my coolant only to have it piss out the side of the block all over the floor as I get closer and closer to first start after the engine change...sigh. Always something.

I am presuming it is a bung for turbo cooling and not a welch plug as the engine was a off the shelf long block from GEM engines.

Greg