Perhaps as a partial answer to Albert de Boer's heartstrings-tugging
query about dual-scale 65/88-note instruments ...

Aeolian shipped a neat tracker bar of ordinary height, with two rows of
holes in it.  A separate switch block behind the tracker bar selected
the set of holes to be used.

Hupfeld used a similar two-row tracker bar, but to switch scales you
had to unclip the tracker bar from the player, invert it and clip it
back.  A separate tracker bar was provided for 73-note rolls.  An
elegant all-purpose solution.

Angelus (as fitted in the UK, anyway) used a taller tracker bar with
two rows of holes.  A sheet of thin leather connected at one end to
the centre of the tracker bar and at the other end to a sprung arm
swung either up or down to cover whichever set of holes weren't in use.
(These instruments also can play top-to-bottom ordinary rolls or
bottom-to-top Angelus rolls, and have two take-up spools!).  A little
clunky but very effective.

I have also seen a dual-scale 'Triumph', which usually were fitted with
Autopiano actions.  This one had started as two separate tracker bars,
trimmed down on one edge and soldered together.  Ugly but probably
effective enough.  I didn't look closely to see how they switched.

Listing all these together makes me realise just how many varieties
there must be.  It sounds like a collecting area in its own right!

As for whether a 65-note stack will operate from an 88-note roll.
Aeolian shipped dual-scale systems as standard for a number of years,
and they work extremely well.  They use pretty big double valve stacks.

The neatest dual-scale must be the later Aeolian 65-note pushups.  Some
of these sense the size of roll put in and automatically switch between
65- and 58-note scales, so can play either organ or pianola rolls with
no switching whatsoever.

As for the merits of converting a 65-note instrument.  Don't!  Get some
65-note rolls instead and enjoy this historic instrument for what it
is.  65-note rolls are very common in the UK, and until not too long
ago were regarded as nearly unsalable.  If the shipping cost were less
someone here could make a fortune selling the things in the USA !

Julian Dyer