You are well beyond DIY now :) Could you not cut a square mortice and tenon instead. I know it's a cheat too but you could epoxy in a 10mm bolt and then use repair care + wedges to level and fill it. Only you would know if you decorate it properly. Get the shoulders perfect on a mortice there and you would have a very strong joint. I suppose it could get fallen or lent on heavily though.
You are well beyond DIY now :) Could you not cut a square mortice and tenon instead. I know it's a cheat too but you could epoxy in a 10mm bolt and then use repair care + wedges to level and fill it. Only you would know if you decorate it properly. Get the shoulders perfect on a mortice there and you would have a very strong joint. I suppose it could get fallen or lent on heavily though.