Well, here are a few thoughts.  Firstly on feasibility: 88-note tracker
bars use brass nipples and rubber tubing as we all know, but the
majority of the early 58-note Orchestrelles (V, W, Francais I) had
wooden bars and elaborate wooden wind ways, so if you were dealing with
a 58-note instrument you would in all likelyhood have to find some way
of connecting the brass tracker bar to the primary valves.

The easiest way would be to cut out the wooden wind way network (which
takes the form of 58 T-tubes, since the valves are fed from both
tracker bar and manual touch box) and introduce brass nipples in the
touch box valve stack and tracker bar and retube with rubber.  You
would have to "octave back" notes outside of the 58 notes that _any_
Orchestrelle can play.

Before anyone reading this thinks I have lost my marbles, however, let
me say I do _not_ recommend this sort of "conversion" -- I just point out
what _could_ be done.

Later 58-note instruments had brass tracker bars, and it would in
theory be possible to substitute an 88-note bar and re-tube.  However,
you would need to find a way of putting an 88-note roll into a 58-note
size cabinet.  88-note rolls are longer!

Now, as for desirability of the substitution:  I am of the opinion that
piano rolls are meant for _pianos_ and very few make satisfactory organ
rolls.  The ones that do are often available as organ rolls, albeit
harder to find on this format.  You could get the same roll for piano
and organ in the later days of the Orchestrelle, I think, and I have
one: "The Bing Boys are here".  The rapid notes and ornamentation are
clearly pianistic, and my opinion is the roll is not a success.

To sum up:  It is almost impossible to do _and_ preserve originality,
very difficult to do on rare later instruments, and musically very
dubious at best (my opinion).

Final thought:  you can easily get some unimportant 65-note _piano_
rolls and cut them down to 58-note width; then you can hear easily what
piano rolls sound like on an Orchestrelle.  Hope this helps.

Paul Morris