It all depends ..........
I just finished add 5 new lag bolts to my 1973 Catalina 27 . The keel is lead . It took me over an hour to lag the first bolt in, and this was after I drilled a pilot hole. Drilling into the lead was no problem. A few minutes per hole. It was a bitch to lag the bolt in. After the first bolt, I paid my mechanic at the marina to use his phnumatic drill , it still took him over twenty minutes to put the bolt in , but it saved my arm. Cost me $50.00 for the mechanic, well worth it. I would not remove the old bolts, but merely add 5 new ones . I also made 1/4" metal plates, about 3"x3" , and ran the bolts through them , to spread the load in the bilge. This must be done while the boat is on the hard. Not really difficult , if you use the right tools. Iron keel is different. You need to drill the hole & tap for a threaded rod. Once again, not difficult , just need the right tools.
