Chuck's idea is a good one although I might be inclined to just make up a whole new keel for as small as it is. And I'd think that you'd want to cast some bolts into the molten lead to attach the flange that Chuck mentions.
That boat is a little beauty. I'm not at all sure that, if I owned her, I'd be so solicitous of my wife. I really shouldn't be considering which is more easily replaced, but....
Another thought occurs. If you do modify this drop keel you may well want to give some attention to the pivot point. It will have an increased load placed upon it and the time to double it up is before wear occurs. And, if not already fitted, you might give some thought to finding a way of securing the keel in the lowered position-perhaps a hole with pin through the keel trunk. With the added weight to the end of your keel, were you to capsize, the keel is going to slam into the keel trunk with much more inertia/force than it would as presently configured, creating damage that could be severe.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.