Jbon, in my opinion, I would not do this in the water. As Psk125 commented, if you start drilling and get some water ingress, you may be in for a real headache. If the original bolts look that bad, I would haul out and replace the original bolts. (yes you will probably need to drop the keel for this process)I’m not aware of Columbia’s build, but the hull may be reinforced where the original bolts are and not as sturdy elsewhere. When completed, not only will you have new bolts, piece of mind, but also a good hull to keel joint.