the keel is there to stay
i agree that a cast iron keel should not be feared too much. last summer while motoring around a point near the 12' contour, our keel must have skipped over a monsterous sized boulder, as big as a volkswagon. it lifted the stern, and my friend at the helm 5' in the air, and scared the hell out of both of us. no leaks were found, so we felt lucky. let me tell you, we never went back there! during haul out time we couldn't even find a dent! i think we lost 2 ozs. of iron. if it was a lead keel, a trip to the foundry for 50 lbs. of the stuff might be needed, as for the rust i just sand, and wire brush the keel, than put thinned out bottom paint for the first coat to fill in all the nooks, and crannys, then another heavy coat to finish it off. thats all! after 22 years , it still looks like a new pair of shoes.