Dear Gordon,  In regards to the number of xylophone bars in a Seeburg
orchestrion, the answer is '22'.  This includes also their largest
commercially produced instrument the Style 'H'.

The nomenclature of '4X' was derived from the Nelson-Wiggen Style
'4X' orchestrion (also with a 22-note xylophone).  Depending on the
roll manufacturer, most, if not all 'G' and '4X' arrangements were
identical, except for the fact that the '4X' was meant to be played
on instruments with 'single-stroke' xylophones, while 'G' arrangements
were meant for instruments with either pipes and/or reiterating
xylophones.

Seeburg Style 'G' :  "When the Red-Red-Robin....."
  https://www.youtube.com/watch?v=pSsrC0Jrwmw
 

Nelson-Wiggen Style '4X' : "When the Red-Red-Robin....."
  https://www.youtube.com/watch?v=fLidiOCWPKQ
 

The arrangements are virtually the same, except that the latter has
a much more animated solo section.

Hope this helps,
D.F. Rowe