Hi, Randolph.  I've only seen one Orchestrelle 'up close and personal',
my own Model W, which still plays 58- or 65-note rolls.  While I can
understand the desire to play newer rolls, I think it would be a lot of
work, though not impossible.

The Model W I have was built in 1899, and the tracker bar is of wood,
fastened to a channeled structure which is fastened to the table, which
is also channeled.  There is no rubber tubing at all to replace, but
then there is no easy way to replace the tracker bar, either.  Bleeds
are holes punched in a fibre disc glued over the table adjacent to the
pouches, and would be easy enough to change, but would be a bear to
adjust, as adjustment would be made with an ice pick or similar.

I do know that the larger and newer models had conventional brass
tracker bars and rubber tubing, which would render them much easier to
modify.  I believe that the only thing other than the tracker bar and
bleeds which would need to be changed would be the roll chucks, and the
ones on my Model W appear to be identical to those in an Aeolian
Pianola (save, of course, the type of roll they carry), so any standard
(or more-or-less-standard, anyway) player piano spoolbox should provide
the required parts.  Before you start, though, be sure that your
spoolbox is wide enough to accept the wider roll.

Because the holes, and hence the channels, of a 6-to-the-inch tracker
bar are much larger (approximately twice the area) than a 9-to-the-inch
tracker bar, the response and repetition speed might suffer somewhat.

Good luck!

Bob Loesch, in beautiful Lake County, California, USA
http://home.jps.net/~rrloesch/index.htm