x2 on bubba. The running temp should stabilize with a 180* t-stat. That is to say, this is the temp it OPENS at; not the operating temp. There have been many many threads here about getting the engine to cool consistently. Generally they come down to purging all the air and the right temperature T-stat.
Tacking on to what bubba wrote above, the warming plate between the carb and the intake manifold that is on many of the 200s not only warms the intake, it also is supposed to provide for a consistent temperature of the fuel mix coming into the log. Many, including me, simply by pass the carb plate and run the heater hoses to the firewall. While this doesn't make much difference in SoCal, where I used to live, it does make a difference in Manitoba or Fairbanks.
Unless you are quite sure that you have found/solved the problems, you might want to make sure that all the air is gone from the system. Typically, you would park on a slight upgrade with the radiator higher than the rear of the car and let the engine warm up from a cold start. Leave the radiator cap off and let the engine run. You will see no movement of coolant in the radiator, then the water will start to move. Often all at once as the coolant finally gets to the target temp. There will be rise in coolant temp just before this point, the it will fall again as cool water enters the jacket.
Let the engine idle for a while longer, until the coolant level in the radiator stops rising and falling, at about 1/2 to 3/4 inch below the lip of the filler. At this point, you cap it and leave it. Best bet, with a new cap that keeps the coolant in place.
Most of us have had similar problems and this technique is pretty much the optimum.