Thinking of a simple way to copy a piano roll to MIDI, it seems like
you could cut 88 slots in a wooden block, put in jeweler's gold-filled
wire for contacts, position it over a brass tracker bar, and as the
roll went through, you would get a contact to ground each time your
little wire dropped through a hole to the brass.

On the other end, take the 88-note MIDI controller (basically a
keyboard with a MIDI plug) and attach the other end of the wire coming
from each contact to whatever the key contacts.  It could feed a
sequencer in a computer.

Cakewalk makes velocity editing as easy as drawing a line, and note
editing in piano roll view is even fun.  I'd try it myself, but my
Seeburg MO has just one roll and I don't think that kind of music is
highly collectable!

Allan Merralls