Yes, a bad rod/broken piston would have a rhythmic "beat" to it, as it would hit on every stroke of that piston. At least thats what mine sounded like. It was NOT random at all, just a nice loud tap tap tap in time as it beat the cyl wall to death.
I think you should just replace all the plugs and wires, then the offending coil pack and you should be good to go. Also may want to change the oil regardless. Can't hurt!
If you want to see if its the coil pack or not you could always just swap it to another set of cylinders and see if the miss follows it or not, but having the rusty post I'd just replace it and move on. Good luck!