Alex,
Top off the tank and bleed any air at the radiator. Run the engine a few minutes and repeat the above (two or three times is usually enough). Make sure that the overflow tank is half full. Be careful when removing the cap.
This method always works on my '71. Some owners have various other methods that they prefer, like jacking up the rear of the car. This can help, but it can also trap air at the rear of the cyl heads.
John
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