Today, as well as attaching all the joints to a control, I started adding corrective blend shapes. The first thing to correct was the throat. As unaltered the throat has a nasty habit of caving in on itself despite my best efforts with goal weights.
Originally it was found that the transformation was probably complicated enough that during the transition the vertices would collapse. during the transition. While my first solution was to add intermediate stages, I had far more success simply building the intermediate stage first. Only needing one which could also provide control over how the transformation takes place.
It dawned on me how I have a lot of bones in my model. But I don't mind a challenge and what I have os far appears to work effectively.
Adding corrective blend shapes was a minor detour since what still remains are a way for the spine to work, and a function that allows Four's eyes to track the eye control nodes.