"Steel" bolts
The 27 had mild steel keel bolts with gelcoat over them until 1978. Then Catalina changed to stainless. The original gelcoat easily came off, leaving the bolts & nuts open to bilge water and corrosion. In many cases, the bolts will be OK once the nuts are removed and the threads are cleaned up. One fix if the bolts are OK is to replace the mild steel nuts with stainless, paint the assembly and let 'er go. Most C27s I've seen need only that. The more radical fix is to do the drill into the keel and epoxy in SS bolts. However, the lead in the keel is pretty soft, and has firebrick encapsulated down low inside the lead, so getting something good to have the new bolts' threads to bite into is an issue. This info is all from prior conversations with those who''ve done it, as well as other published info. My '74 has mild steel bolts & nuts with surface rust, but are still structurally good. So I keep an eye on them and paint them every couple years with one of those paints that turns rust into primer, then with bilge paint.