Cal 20 keel bolt nut replacement.
I changed out my keel bolts on two different cal 20s. Do one at a time. In your case, it sounds like you just need to remove and replace the nut. I would first try penitrating oil and let soak for a couple of days, then try a socket and see if it the nut will come off. If not you may consider using a torch on the nut, this will expand the nut and hopefully allow you to uninstall the nut. You can cut the nuts off the bolt, with either a sawzall or an abrasive cut off wheel. In either case, when you do get the nuts off use SS replacements and put some grease on the bolt threads. If you find that you need to change out the bolts, do one at a time. I used a sawzall and wacked the bolts at bottom of the nut. Then used a long drive punch and the impact caused the filler to pop off of the bolt head at the bottom of the keel. I hope this helps.
Past cal 20 x2 owner
Present Cal 2-29