make a jig to hold two bolts square to the keel and pour the lead keel so the bolts stick out the top, drill two holes up into the wood and epoxy the bolts up into the wood structure. you'll probably have to scale it from the picture , there is a design ratio but it's for actual yachts and assumes you'll have furniture and stuff in the boat. Pour on the heavier side and leave the fastening bolts up about the midway point so if you want to after a test sail, saw off a portion, or conversely glue on another lead bit and fair it in with thickened epoxy.
some people will drill through the lead 'shoe' and screw the shoe onto the wooden keel portion , that way you can make more than one shoe and swap them out to find the right one. Once you find the right one you can make it permanent .
To fasten a keel onto a model boat with a strut keel as shown in the upper picture use threaded rod from the bulb up through the strut and put a rubber washer and nut in the bottom of the hull.
*shortcut to know if your pretty close , the boat should float to its waterline. once you make the hull and are ready to make a keel , put the boat in a pool and using a variety of weights (wrenches, or sockets) pile them on the center of the deck till the boat is floating to her lines. Remember you'll add a bit of wieght ( but not much) adding the mast and rigging. Weigh all the crap you sat on the deck and that's what the keel needs to weigh.