Ernie,
They're a son of a gun to get out. I had two bolts that were stubborn and it seemed like it took me hours. I used WD-40, I applied heat to the metal of my screw driver with a blow torch as I held it on the bolt head, and I used an impact screw driver. An impact screwdriver is hard to bang when your under the keel trying to hit it with a hammer.
I finally got the bolts loose to a point where I got them to unthread about 1" so I kept screwing it back in and unscrewing until I finally got it out.
If I had to do it over again I would use an impact cordless electric drill with a Phillips bit of the end. Makita makes one with an adjustable clutch on the chuck.
I had a short 1/4" Phillips head machine screw at the bottom of my mast that held my mast plug and top hinge in place. The head of this screw was large enough to take the largest Phillips screw driver I had in my tool box. Do you think I could budge that screw? I tried everything I had including channel locks on the screw driver.
My kid came down the house and said, "Dad, what are trying to do?" I said, "I can't get this friggen screw out." "I've been at it for over an hour now." He said, "I can get that out of there in no time flat" and he went to his pickup truck and came back with his Makita cordless impact drill and he put a large Phillips bit in the chuck and took that bolt right out in no time flat.
Just be careful that you don't break any bolts when you're trying to remove them. Take it slow and easy and they should come out. If you do break one you can always drill it out. I'm told that there is a large metal plate embedded into the lead on both sides of the keel slot. I think Rudy said it was made of Bronze, but I'm not sure. Good luck!
Joe