Shedrock, I do the same as Jon suggests. First I caliper the stone head to verify the thickness. Then I'll use a bandsaw or hand saw to cut a notch in the shaft. Go slow so you can center the point by trying it in the notch repeatedly. When you have a great fit then file and sand the end of the shaft to get a good taper on the end. Epoxy, insert head, wrap with sinew, recheck for centered and let it set up.
If you want to do it the primitive way this is a video of a guy I know who really knows his stuff!