Where are you picking up your inlet coolant from? If youre drawing you water from the top of the motor, youre getting the coolest water/coolant. Find where the coolant leaves the block and goes to the radiator and try to tap your heater there.
Try a 210* thermostat to see if your heat increases.
Id buy a Factory Chassis Service manual(not haynes/chiltons) for your car, usually not to expensive online. It will describe the vacuum routing and door operation of your heating system, plus everyother component of your car.