Keel bolt issue
Actually, there had been very little ''cast iron used in this country since WWII. Most of what we call cast iron is low carbon steel. Low cabon steel is more rust prone and more electrolytically active than cast iron. When you cast J-bolts into cast iron the cast iron and bolts contract on cooling leaving a small crevice around the shaft of the bolts which permits corrosion. Replacing keel bolts in any iron keel is a tough proposition, been there, done that, wore out the tee shirt, but it is especially difficult with a keel that has J type bolts. If you were to use bronze bolts you would have three very different metals present, mild steel, higher carbon/higher strength steel (from the old bolts)and the bronze. That makes a near perfect battery. I agree with you about either using SS or Galvanized as perhaps a better choice than the bronze but, of course, what I am sure that you meant to say is that Monel would be an ideal choice given the various metals present.