Water in oil after rebuild - looking for guidance

Magnum engines never used the pins on the China walls, but if the intake gaskets were not positioned correctly maybe there could still be a similar problem.

That is a lot of coolant in a short amount of time. What front accessory drive system and timing cover are you running? Was the timing cover very corroded around the water pump area before assembly?

Worst case scenario, did you accidentally run a long bolt into the wrong hole when installing the timing cover? One of the lower holes on the left front of the block can cause this.