I've only tore down about 10 engines in my career as a enthusiast. I have never seen a lack of casting material like those. Usually it's the opposite, some extra flashing material that can be ground of to make it pretty or to help the oil flow ever so slightly better. I'm not saying they are not good cores, I'll let the more experienced chime it, but I would not consider them for souped-up build. You might ask "why" and I'd have to say because "I don't know any better". Even if they are good-to-go, perception of a problem can reduce their value.