You have a pully problem and an air problem. Water or air in the water pump will not throw a belt - it is pully alignment. When you throw the belt, air goes to the top, temp is steam temp in noncirculating system - lower than the metal parts - and you have severe overheat - not shown on water temp and delayed on
oil pan temp.
Oil blowby suggests ring damage - can rebuild in situ and compression check later, or pull now - ask KCR about odds.....
Another possibility is that boiling water in the
oil blew out the overflow ~ better