318 or 360?

In my experience, only if mercilessly overheated. I hear cracks between thinnest parts between the valve seats are a common place for cracks. As far as heads go, I would wait for the Black Friday sale from speedmaster. Do you really need aluminum heads for a cruiser? No, not really. But compare the cost of getting a set refreshed at the machine shop vs a pair for 40% or 45% off, and aluminum starts looking very attractive