I joined this forum today after reading of the similar issues with your c-30 boat.
Hope this helps. I had similar worries with the keel on my 1972 C-30 hull number 036 which I purchased in 2015. I contacted another forum's membership and got really lucky in that a response (one of many) cam back from a chap who actually worked at their Californian plant alongside the very production line my boat came off.
I also contacted Vince Valdes, son of Dick Valdes who was the builder back in the day and Vince sent me the keel diagram which he unearthed from their archives.
I have since managed to purchase all of the blueprints I needed from another website whose name I can provide for you if required.
Back to the issue though.
My keel had a horrid crack running longitudinally along the starboard side just around the fairing of the keel to hull area (the curved portion). My boatyard figured this was simply due to hull flexing and may need to be done occasionally as a matter of course. The bolts themselves looked quite bad but were covered by the nuts which looked equally bad, so it was hard to tell just how bad it was.
I lost many nights of sleep worrying about my keel falling off as well, just like you probably have.
We had the boat hauled out for a few months that year and did lots of upgrades and repairs including grinding out the cracked are, filling with epoxy and finally glassing it over to a smooth finish again. The fellow from the forum who worked on Columbia's production line gave me the courage to go ahead and take a look at the keel bolts whilst the boat was out and just as he had found with his Catalina 30, once he had removed one bolt, he discovered that the bolts cleaned up quite nicely and were not so bad after all. I went ahead and had my boatyard do this and took photos of the before and after to prove the work was done. Surprisingly, he was right and mine did not appear as bad as they looked, once cleaned up. My boat does not have channel iron as shown in the drawings but has 1/4 inch thick galvanised steel plates 6 by 6 inches square at all 9 bolts. The forward end of the keel has a transverse plate just ahead of the mast in front of the door to the head.
If you want to email me directly off the forum you can do so at email@example.com
Here is the drawing I got from Columbia Yachts in Costa Mesa, CA