So, there’s always a short cut, and a proper way to do something – what you can see here is the top diff-cradle bracket. My problem was the clearance between the bracket and the chassis wasn’t sufficient for a lock-nut and using two thin nuts jammed against eachother isn’t a good solution.
So, given that, I’ve cross-drilled it and used a split pin. I’m also pretty pleased that the bolt shank to thread transition happens just through the bracket on the right, which you can see here. According to Carrol Smith, this is exactly the transition point.
So, I engineered it properly.