While not an easy task, 4130 and a GTAW will do it. Just be careful to clean all the corrosion out first, anneal the metal so you do not get warp cracks, and heat treat back to the original test hardness in an inert enviroment. How deep are the pits and where are they? You may be better off to just hog the whole area out before filling. This is not a small job by any estimate, but certainly a good winter project that will take up the months.