I removed the mount upon which the stop levers are located and this allows for the removal of each key for cleaning.
A few more pencil markings were found on the keys: "#49"
I gently sanded the sides of the keys to remove any finger gunk. I then used warm water and a small amount of light detergent on the ivories. Finally I used "0000" steel wool to buff them up.
I think they ended up looking pretty good.
There is still a fair amount of discolouring, but I am told that with some sunlight exposure, they will whiten up a bit more.
Here is a before/after picture after the top octave was cleaned. Quite a difference, but you can still see the extent of the yellowing, especially on the high "C".
I will have to track down some ivories fronts for the half dozen that are missing.
The black keys are generally in pretty decent shape.