Hello blackjohn,
We did the repair you might use on our Catalina 27 many years ago. The boat has been sold and surveyed two or three times since the repair without undue concern by buyer, seller, or surveyor. Check with Catalina. The person I talked to was helpful, explained the process, and sent the ss lag screws for the job. I think they included a drawing to show recommended locations for the lags. This is a good project for asking help from your sailing buddies who do not own a boat and enjoy sailing with you.
As I remember the drilling for the lags was the difficult part. Heavy duty drill needed. LONG bits to reach into the bilge and deep into the keel. Extension for the ratchet and socket. PATIENCE is the prime requirement. Our job required an 8 hour day, but I'll admit that included driving to the hardware store several times for bits. The bits loaded frequently with lead and had to be reversed to remove them from the keel. I also remember places in the keel where the solid lead "curly" material coming out of the bit changed to a grit. That was disconcerting, but I had no way to know what I would find.
Also, after the first bit of fiberglass was drilled through in the bilge we found wood that appeared to be yellow pine or something similar.....bright yellow color and sap. I don't remember whether we used a lubricant on the lags, but I do remember twisting them in a bit then back out to clean the threads as they cut into the solid part of the lead. There was no such thing as just cranking the lags in with brute force. We also used ss fender washers in the bilge and put sealant in the top of the drill hole and under the washer.
Best Wishes, Phil