I have an '81 FJ40 with a GM 350.  I am installing aftermarket heaters front and rear.  I would prefer to be able to use cable operated heater valves to contol water to each core.  I know this may be a bit of over-engineering, but that's just me.  If I take one hose from the water pump, should I tee off from that and send two lines, one to each heater valve? Or is there a way to run two separate lines from the engine and have two separate returns?