Getting into the setup it soon became apparent that the neck angle was wrong, these guitars are well known for the neck pocket failing due to the way they were constructed. When the correct neck angle was set, it left a large void in the neck pocket. The solution was a shim to support the neck.
When the neck was removed, there was already a small cardboard shim fitted, and upon removing that, it became apparent that the base of the neck pocket wasn't flat, leading to a more complicated shim.
A rosewod shim was cut and thicknessed, constantly checking the angle of the neck, at the same time, the neck pocket was glued back together to the lifting top, to prevent the neck pocket sinking any further.