The fire-hole ring rivets being removed prior to replacement.
Inside the firebox showing (next to the screwdriver handle) lap-seam rivets whose heads have burt away. These will be replaced with patch-screws. The joint at right-angles is where a replacement half-side was fitted at some time past.
New valve-spindle guides have been fitted. (These are the two bronze bits whose ends can be seen each side of the motion bracket.)