[empresley]

Medic,
Since we purchased the '84 I keep eyeballing those end pieces and I know something will happen, like you I am not sure what. I took some time late one evening and explored almost all the members photos and made mental notes of those interiors from the 50s and 60s and any that had been modified. It was not a complete waste of time. The older models had a much simpler cabinet style transistion before the use of molded material.
If done carefully and with attention to detail, I don't know why a cabinet style replacement would not work.
This will be hard to describe but I am leaning toward, and will work on some sketches, a combination of curved vertical pieces (matching the ceiling curve) and transistions with horizontal panels or soffits. All wood, stained to match the existing window valance. It will have to be in "steps" to maintain head room. I think we would enjoy the warmth of wood and like looking up at stained veneer with recessed lighting more than the existing plastic.
This is long range but I thought you might like to know someone else is considering a change. If something definite comes off the drawing board I will post the idea.
In the meantime, if you need a template, I would suggest buying a sheet of thin luaun plywd. and with the help of cardboard, make templates to match your ceiling.