Three words DON"T DO IT. Unless you have a closed cooling system.

Never had an issue, unless you are boosted or doing EXTENSIVE portwork I don;lt see advatage to the extra cost of aluminum, unless salt...

I did AFR on my 540's, looking back the extensive cost could have been saved with iron heads people think aluminum make more power but they flow same as cast if same head and spec, or massage to liking..