> ... we are not getting enough sustain on the high notes ...

One easy way of obtaining longer ring times is the use of resonators.
A tuned resonator, acoustically coupled to the bar, will noticeably
extend the note as it does for instruments like the marimba and celesta
("Chrysoglott" in a theatre organ).  Ordinary PVC pipe will work just
fine.

Where will this "life size" music box be shown publicly?

Regards to all MMDs,
Al Sefl