If the "stuff" in my photo is a 1/2" steel plate that was attached to the bottom of the stub during layup of the hull with 5200 or a thickened epoxy mix and then glassed over, as would be necessary, before attaching the lead, it is one hell of a strong keel stub. I have been looking at keel stub construction in boats under 30' and have found nothing approaching this.
Do you have the "bead" of "sealant" running around the perimeter of the floor of your bilge? Mine was painted white and there were remnants of a layer of resin over the steel. The "sealant" looks like it was squeezed into the bilge around the stub's edge as things were tightened up.