The hole(s) in the water pump is for the return line from the heater to the cooling system. The hot water comes from a fitting in the cylinder head to supply the heater. The only reason for a second port in the water pump was to accomodate a special bypass-type thermostat on the heavy duty engines, one that's no longer in production.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!