As long as your engine isn't overheating the H20 pump should be just fine.
According to my '73 Service Manual you also need to have vacuum on the heater water valve under the hood (middle port-"green" at the valve) to 'open' it for coolant flow to the heater core as well as the AC/Heat door in the plenum. You said you already had vacuum to the "blue" hose...that controls the AC/Def vent. You also need to connect the (assuming you are doing this at the dash controller) "brown" and "yellow" to the vacuum source. This should get you heat at the floor, providing your temp cable is functioning properly(it operates a vacuum switch on the plenum to control the H20 valve. I'd be happy to answer any more questions if you'd like to email me.