This topic has been covered in two bouts in MMD, which at least covered
the Themodist and Duo-Art differences.  Summarising these and adding
Welte to the list gives the following :

1. Originally, 88-note Themodist pianos were shipped with stacks
divided E/F above middle C, giving 44 notes each side of the split.
Hupfeld 88-note rolls have the same split point.  Early Aeolian and
Hupfeld rolls have the split printed on the roll to aid Pianolists'
use of the solo control levers.  My 1909 65/88 player naturally applies
the same split for 65-note rolls.  The 65-note scale omits 12 bass and
11 treble notes so this gives a 32:33 split.

2. Duo-Art pianos (inexplicably) have the split one note lower at D#/E,
giving a 43:45 split on the keyboard.  The system plays 80 notes,
omitting 4 each from bass and treble, giving a working split of 39:41.

3. From earlier MMD postings, later American Themodist instruments
appear to have adopted the Duo-Art split, presumably because they used
the same stacks.  There is some suggestion that later Themodist rolls
accent the ambiguous E with snakebites in both treble and bass, a
practice that ought to be adopted today when anybody makes accented
rolls.

4. Ampico split at E/F, giving a 44:44 keyboard split.  The system
plays 83 notes, omitting 2 bass and 3 treble notes, giving a working
split of 42:41.

5. Welte split at F#/G, giving a 46:42 keyboard split.  The system
plays 80 notes, omitting 3 bass and 5 treble notes, giving a working
split of 43:37.

Looking at what technical information I can find, it's notable that
none of the literature states stack split points, even when going into
great detail about every other aspect of the tracker scale.  Now's the
chance to fill in details for all those other split-stack systems!

Julian Dyer

 [ Thanks, Julian, I will place a summary of this elusive data
 [ under "Music Rolls & Tracker Bar Scales" at the MMD Tech site,
 [ http://mmd.foxtail.com/Tech/  -- Robbie