In the few email exchanges I have had with the Museum of Anthropology in Columbia Missouri, I have gotten the feeling that they are really great people. I can see why Dr. Grayson chose be a benefactor to them with his incredible collection. I'd encourage you to contact them with all the details, if the offer does not fit their collection plan, I am sure they could put you on the right track to the best place for your donation.
I'd love to own those bows, but like you, I agree that they are best located where they can be best conserved, protected, and available to the public. Thanks for sharing.