Thanks a lot to those who gave comments, here or in direct emails.
Maybe I should answer Craig's question, "What is it about the Sankyo
movement that is not acceptable or sufficient?"

(a) The Sankyo movement does not play by itself, but must be cranked
-- which is quite unexpected for people who think that you wind up a
music movement and then listen to it.  And as a musician, I must say
that this _is_ a huge difference.  When I have to "work" (a crank;
on a crank organ or a music movement; or e.g. the keys and pedal on a
church organ), I cannot enjoy the music in the same way as when I only
listen to it.  Yes, "making music" is also nice, but it is definitely
very different.

So, regarding this issue, the question is: Has someone already
"motorized" the Sankyo movement -- with a spring motor working for four
or more minutes, or maybe with a silent electric motor.  (Yes, of course
I know it can be done in principle; I can design the necessary gears
myself, but has it been done?  And how much did that cost?)

(b) Also, yes, the music would have to be continuous for the piece.
A motorized movement with a continuous (Leporello) loop would need
a switch-off function in some way (e.g., a cutout on the side of the
paper strip with a switch or a suitable mechanical stop).

"Sectional playing", i.e. having pauses of 1 or 2 seconds, is not okay
unless the gaps are at the positions where the piece has a G.P. [Grand
Pause] (but I think these are not at nicely dividing positions).

I did not ask my client about her "reasonable cost", but I would
estimate a few hundreds (be it euros or $ or £), certainly below 1000
is the maximum.

With these constraints, is it possible to put it on a cylinder music
box?

Thanks for considering my question!

H. Müller