Take off the radiator cap and see if the water level changes appreciably when you rev up and slow down the engine. If it does it's likely you have a scaled or partially plugged radiator. Watch for bubbles coming up to the radiator neck which is an indicator of a leaking head gasket which can cause over heating as well as other problems. If you have an Infrared non-contact thermometer (inexpensive at Harbor Freight) you can look for hot or cold spots on the face of the radiator which is a good indicator of a plugged radiator.
The good thing about the 1200 radiator is that it's repairable being soldered together out of real metal instead of aluminum and plastic like later GW models. Any decent radiator shop can rework one of these.
The good thing about the 1200 radiator is that it's repairable being soldered together out of real metal instead of aluminum and plastic like later GW models. Any decent radiator shop can rework one of these.