tired keel bolts, iron keel, sister or drop balast? 50 ft wooden

Fellow members, I'm trying to figure away to add another mast to the back of our new 1961 50ft wooden sloop....but in the mean time I have some keel bolt issues. I have talked to three expierenced men and each have their own very logical opinions....one says drop the keel... punch out the old bolts, one says drill the old bolts out.....replace bolts without dropping the keel and the third says sistering is the answer.....going down about 4 inches into the cast Iron keel....now these three gentelmen are the best but I have to make the right decision....would anyone like to be the 4th or 5th or better yet share their expierences with me to help with this decision.
John Jablonowski