Mmmm ... both of mine only need the centre pipes removing, which wiggle out of the collector after undoing the stud by the manifold.
I was told I had to remove the whole system so my first oil change was a bugger. That's when I noted the collector box was rotted so had to order a new set of downpipes and collector. I have done it that way since.
The pipes sit just off centre so the bolt in the Williams plate is just out of line for a socket
I note your comment on the bolt loosening off, so will check regularly