Most likely you poped a head gasket. It doesn't take much on a 496 to do it. In the future, if you get a high temp alarm, STOP immediately. Shut the motor down and do a check of the water intake. You would be suprised how little grass or weeds it takes to cut off water flow. BTW it only takes a short time fot the rubber impeller to disintegrate from no flow.
Darrell.