I'm suppose to be putting things back together but I seem to be working backwards.
Took the arch linings out and gave them a good scrub. Never ending stream of brown water coming off them so gave up after half hour. They're good enough.
The boxes behind the arch linings were a little corroded so gave them a going over. From what I can tell their only purpose is to give the arch linings sonething to secure too via that one hole in the middle, but they're held on by nine bolts! The little grill inserts are easily popped out with the linings out so I'll give them a good clean up along with the holes they sit in. I re-tapped some threads for the arch lining bolts ready for the new bolts and washers. They'll go on with a smear of copper grease so they shouldn't corrode up again.
Tomorrow I'll start moving forward.