You are looking for 2 buds above the graft and enough wood below the good bud to make a simple bevel cut for Bark Grafting and a little more is needed for Whip & Tongue. Look up Topworking Pecan trees on YouTube for bark grafting videos. I have done Mayhaws, Apples, Pears, Pecans, Persimmons, Plums with a bark graft. Sap must be flowing (bark slipping) except Pear trees. Pear trees are so easy to graft I think you could just throw the scion at the trunk and it will take. After grafting a while you develop your own technique. My pecan grafts are over 95%. I have topworked over 200 pecan trees. So you figure out what works for you.