340 runninng lean and overheating

Don't know if your car came with a reservoir tank or not. Under your radiator cap there will be a rubber hose. It will go down the side of the radiator or it will go into a white/clear plastic tank. If it goes into a tank, the cap is special, and the radiator gets filled fully. If you don't have a tank, leave an inch of air space above the coolant. There was a flat plate under the rad. cap that showed the cold coolant level.

When changing coolant, fill the coolant leaving a 1'' space, run the engine till the thermostat opens. The coolant level will suddenly drop. Add coolant as above.