Re: Keel weight
This is designer and engineering territory.. the hull and reinforcements would have been designed for a certain weight/righting moments of the original keel.. attaching a heavier keel could cause issues. I think you need to tread cautiously here....
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"