Thanks to all the people who responded to my previous posting,
including the gentleman with a collection in the US who has an
identical instrument.

I hadn't previously appreciated that there was an early connection
between music rolls and the Mason and Hamlin organisation.  The
Automatic Music Paper Company, the first to manufacture music rolls
commercially in the USA, began manufacture in 1877 in workshop space
rented from Mason and Hamlin, in a part of their factory near Boston.
The AMPC were supplying, among others, William Tremaine of the
Mechanical Orguinette Company, the founder of the Aeolian empire, who
bought them out the following year.

It is then perhaps not too fanciful to imagine that Tremaine, wanting
to experiment with building a roll-playing reed organ somewhat larger
than an organette, might have obtained some instruments from Mason and
Hamlin, and adapted them.

It is frustrating that I cannot find a serial number on my instrument.
The only guides to dating it are the characteristic 'Gold medals' over
the keyboard, which seem to have been added to every couple of years or
so;  My organ has 6 of these, 3 each side, and the latest date there is
1881, so perhaps this is, after all, a particularly early example of
the genre.

Rowland Lee
UK