Keel bolt issue
I have a question regarding what to do about my keel bolts.
I have a 1978 Catalina 25 with a cast-iron fin keel (1900 pounds). The keel is attached with 6 half-inch (I believe) mild steel bolts, attached with nuts in the bilge. The existing bolts are so rusted and flaking that not only are the threads not discernable, but large chunks of both nut and bolt have flaked off.
I do not know about the internal structure and reinforcement of the hull area to which the keel is atteched, but if anyone knows, please tell.
I''m pretty sure that this situation represents a problem, which I would like to fix before the keel joint starts leaking. My thought is to drill and and tap through the bilge and into the keel, then screw in bolts from above. Is this a good idea? How many bolts, how big (length and diameter) and what material (stainless doesn''t rust; mild steel is galvanically compatible) would be best?
The textbook solution seems to be to drill a hole from above, then drill a horizontal window in the keel to take a nut. This seems like a lot of effort in a cast iron keel; is tapping the keel itself OK (and feasible)? Any thoughts are appreciated.