That slapping sound you just heard was my hand smacking my forehead. Of course, a magnet will give an instant ID. The other cues are good to know, too, in case I'm someday pawing through a bin of mixed engine parts.
Interesting that Chrysler didn't consider freeze plugs to be necessary. I'd have thought that aluminum would be just as susceptible to cracking due to frost pressure as cast iron. I lost a Buick nailhead that way, long time ago.