I think you are going to have to persevere. The reason? The o ring gasket between the end of the cat and the manifold will need replacing. I had to reuse mine pending getting new ones and one blew really badly.

If you have some old sockets whitworth or AF you might find something that you can "hammer on" by testing on a nut you have taken off already. More plus gas. Also watch out for falling sockets! I got one right on the bridge of my nose doing that job.

Two man job doing the gearbox but you know that.

have'nt had the socket in the nose but have had the torque wrench in the nuts.
but i wont be beaten by 1 nut