[Beav]

The loss of heater heat would have been a result of an air pocket passing through the heater.

How soon does the water begins to spew? Before the engine warms up, or does it need to run several minutes first? If it is while the water is still relatively cold you probably have a compression leak. If only after the water is hot you may have a water pump not pumping (pulley or impeller slipping), or a severe blockage - mice or mouse house in the old radiator? Collapsed inner hose layer? Check the temp of the upper and lower hoses when it begins to spew to see if there is a large temp difference.