I don't have a GearBox, but I can tell you from an engineering point of view those brackets are bent too much. You need to have washers or spacers under them so that the locknuts press flat against the bracket.
If you need to ensure that nothing slides around, you're better off using a layer of rubber (which is compressible as well as friction-inducing) wrapped around the black square tubing at the bracket location. That will help ensure there's adequate tension on the bolts without deforming any metal pieces.
Engineering: Finding complex solutions to simple problems you didn't even know you had.