Thanks for the replies everyone.
What do you think about covering the tops of the worst bolts in 3m 5200 adhesive/sealant? Since the repair options seem to be to either destroy the worst nuts or add new bolts, I'm not sure there'd be a disadvantage to covering it up with 5200.
My goal would be to prevent further corresion, and perhaps help hold what's left of the nuts together to keep whatever strength is left.
Lastly, does anyone know where I can find out if my keel bolts are imbedded in the keel or go through to the water? I'm trying to figure out if I take one nut off, if the bolt will drop out and flood my boat or if I can take one off at a time while it's in the water? I have a cal-20.