Jeff Bridges wrote, "... I want to be able to use a computer on it."

Zowie!  The short answer is that you can't get there from here.

Some energetic souls have converted Hammond organs to _transmit_ MIDI
by borrowing a set of key switches, but for it to play via MIDI is
essentially impossible.  Well, it could be done, but it's easier to get
to the moon.

Here's the problem:  The Hammond is a true spectral synthesizer.  The
drawbars adjust the amount of a given spectral component to be added to
the soup.  Two subharmonics, the fundamental, six upper harmonics, for
a total of nine.

How did they do that in 1937?  Laurens Hammond was a smart fella (and
the patent literature on the Hammond is a true wonder to behold).  The
tones are generated by rotating rods with dozens of serrated wheels on
each rod, with a magnetic pickup to make the current.  The rods are
driven by a large synchronous motor (Hammond got started in the clock
business).  The summation of the harmonics is accomplished by having
each and every key attached to a _nine_ pole switch.

This adds up to well over a thousand analog gates that would have to be
individually wired into the rig.  You could, of course, buy a new BX-2,
which is already MIDIfied, but it would not hum, scream, and smell like
an old man's house.  The ideal solution would be an Aeolian Hammond
model BA player organ and some pneumatic valving.  That design got it
right.

A. B. Bonds