making a keyway is a nice repair. its tricky to do. with epoxy pinning properly done and clean concrete, bonding agents and the right mix will make it very strong. jagged concrete actually has more bite, clean cut concrete has less surface area. its just like ice, crushed ice cools faster theres more surface area than cubes, same theory applies to concrete. You can just as easily make the bond beam very fat like double wall thickness and pour it down the back below the existing wall and tie in the rear too with epoxy, this prevents pushing from sides. just have to really inspect the existing shell for condition, you wont know til its cleaned up well how the surface and core is