I guess I'll jump in on the jumbo rolls discussion.  I bought
some of Frank Adams' AMR rolls and they almost fit the spool box.
Removing the bottom board from the spool box gave the extra space
and they play just fine.  Now I have a very dusty set of tubes
leading to the tracker bar.

Regarding front oval shaped pins which guide the key in its up and
downward movement, when I first noticed the oval shape I assumed it
was made that way in order to adjust the side play of the key.

I asked myself, why else would they make it oval?  If it was to
increase the mating surface (as opposed to a round pin), they would
have made it oblong (rectangular) with smooth corners.  If it was
meant to stay fixed, they would have been oval from top to bottom.
If they were rounded where inserted into the wood holder it would
seem to be meant to be adjusted.

And, for Bruce Grimes, it would help to see a picture of the spool
box described.  What was the rationale for changing the location
of the Duo-Art mechanism after years of placing it below the piano?

Bill Chapman - in c-c-cold Palm Springs, California, where it
didn't get up to 68 degrees three days in row and dropped to
a furnace-shuddering 43.