I have 1970 MKII with original keel bolts. The nuts are stainless steel and we’re replaced at some point. Like yours, the bolts are also rusted but have been holding on for 52 years. My boat is in fresh water, which ads some life. I plan to replace the bolts within the next few years. Hope that helps.

Yo! Getting mine inspected here soon . 1969 Columbia 26 . They’re hella rusted and might need to be replaced soon.