I would suggest first removing the reproducer, wrapping it well in bubble wrap, then putting it inside the horn, with plenty of packing around it. Secure the carriage with rubber bands, to keep it from moving. Put packing - foam blocks or similar - inside the case, to support the motor and keep the horn from rolling around. The crank can go inside the case as well. Cover the case with more layers of bubble wrap, and secure them well with packing tape to keep the lid closed tight.
Then put the machine in a heavy cardboard box, with several inches of tightly packed padding all around: you don't want anything to move around in transit. Some rigid foam panels against the inside of the box would be good as well. Tape the box up tightly, mark it FRAGILE - MACHINERY, and insure the hell out of it.
It may be time-consuming and expensive; but it beats the buyer getting a broken machine.