...
A large gift of microfilms was presented to Isham by Professor John Milton Ward IV. There is a blog post about these here: http://blogs.harvard.edu/loebmusic/2011/01/05/john-ward%e2%80%99s-treasure-trove-of-microfilms/ The post includes a PDF inventory.
Microfilms sent by Yale for the 2008-2010 Mellon-funded cataloging project are now shelved in rows 4a and 4b of the Cage. There is an inventory in SharePoint.
Manuscripts
Here are some ideas for how to discover music manuscripts at Harvard:
...