Torque Strap?

i'd weld a nice thicker washer to the outside and then notch it to match. your 'weak' spot is now at least double the thickness so plenty strong enough and no need to spend and money.
neil.
ps what is the notch supposed to clear? got any pics? maybe shave a bit off of that so the notch you've made won't need to be so 'deep'. share the clearancing as it were.