Charles Davis wrote, "I just feel that the wheel-type of crank
will help it to crank more smoothly (easily)."

I can't remember seeing a Hofbauer 20 with a crank-wheel.  I do
not think they were ever a standard accessory.  I think that wheels
are generally found on 36-note and larger organs.  The most likely
source will be a flywheel handle found in a flea market, and it will
probably be necessary to make some sort of adapter.  It's a good
idea, but...

As to the tarnished pipes, I agree with Dell Urry that you almost
certainly have brass pipe tubes with damaged lacquer, and that you
can polish and re-spray them.

If you need to get further into the organ, see my notes on
http://www.wallace-venable.name/mechanical-music/Hofbauer-20/ 

Wallace Venable