You might try to bolt a strip of material like Delrin to the bottom of the keel. Delrin is a very durable kind of plastic often used for cutting boards and bearing material. You might be able to cut a thin strip, the width of the keel bottom and maybe 1/2" thick, drill holes in the Delrin, through the keel and bolt it in with a backing plate using silicone sealer on the bolts to prevent leaking. Countersink the holes in the Delrin so the bolts don't get ground down. While you're at it, make a few of the Delrin strips so when one gets ground down you can bolt another in it's place. You would only need to make one backing plate.
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