Preparations for tackling this major patch are going well.
The area of the repair has sunk quite a bit, so to improve the arching, the treble side of the cast needed a fair amount of scraping. The contour tool helps by tracing the concave curve across and then pointing out the irregularities when turned around and put I the same position.
The next step will be the removal of the current patch.
Never forget what great work you do, Dr. Carr!