Speaking of case hardening, it can be done with an OA torch with a carburizing flame (a yellow trailer past the blue part). Not sure I'd try that on rocker arms though.
I did that once when I built up the brake pin slide surfaces on a Model A. They are just plain steel and after eons of use get a divot worn in them, which cause the brakes to be even more inadequate than they normally are. I built them up with a torch and was going to mill them down smooth, but the cutter wouldn't touch them. I wound up smoothing them with a Dremel grinder. It worked and I had the best mechanical brakes of any Model A around at the time.
The perfect profile on a rocker arm tip would have to be ground somewhat like a gear tooth involute pattern. But more complicated for sure.
