coolant in oil on 2003 Chevrolet Malibu

Just rebuilt engine- runs but rough shut it down.
coolant in oil
Heads were reconditioned, new gaskets, thermostat was replaced.
exhaust was light blue/steamy
Is this a cracked block or head

Asked by for the 2003 Chevrolet Malibu
Normally, this would point immediately to a head gasket leak. If that's not it, then it may be a problem with the heads or the block.