Pulling the freeze plugs is good advice and while you're at it....take out the block drain cock at the driver's side rear of the engine and run a coat hanger up inside the block. This passageway is usually full of almost solid crud that even hot tanking won't break loose. Once you get this passageway open you'll be able to get more rust/crud out.
Just a suggestion.....use only distilled water and antifreeze in your engine and you'll note less buildup in your radiator. It's worth the $2.50 for 4 gallons of the distilled stuff.
Dave
