I think the original ribs are stamped.. as heavy as the metal is, it must have been a hell of a stamp/press thing (and probably expensive) which is likely why the repros are smooth.
I don't know how you'd put the ribs on an aftermarket running board.. but if you figure out how to do it cheap, you could make quite a few bucks buying the repros, putting the ribs on, and reselling them!
