5wests has the right idea.I would sand blast, any really badly pitted spots can be brazed up or filled with lead. This is the way body work was once done. you could also use MAR-Glass ( has other names it's a reinforced type of filler, thats the filler 5wests is talking about) is good over pitted areas. It's better to use something that will give it a little rigidity hevily pitted areas are probably thin straight filler will blow out over time
