Let's see; freshening a 318, no racing/nice cruiser- and you think you need new aluminum heads? You'll likely never be running a cam that can make use of your shiny new heads, and need to swap out the supplied valve gear anyhow. 302s are a good option, but you need the right pistons to take advantage of the quench. And to say they're all cracked- is this from personal experience, or just heresay? I've yet to have a cracked 302 (not saying it can't happen, ANY head can crack. Even aluminum)- 308s (and Magnums) are a different story. I think people confuse the two.