From Vaughans notes, with my own expansions:
Name of institution
This should probably be kept in the "publisher" field. We need a standardized name ("Washington and Lee?" "Washington & Lee?" "W&L?").
Name of Repository
Hmmm. I'm not seeing a field that leaps out as a logical place to put this. We could make it part of the description?
Name of collection
I'm not sure this should even go in the metadata, because we could actually use the name of the collection in the real world as the name of the collection in Dspace, where it would serve the same purpose.
MSS number of collection
Most logical place I can see would be an "identifier" field. These fields are usually used for numeric identifiers that are unique to the item, though (examples would be the ISBN number).
Are we sure we need this? If the document is available on the web, why does it matter to the user how we classify or organize the physical material? Ideally, they wouldn't even need to access the physical version. Ever.
Date of Document
I'm assuming this refers to when the letter was written. Given that, the best place would probably be the "date.created" field.
Identification of document
Is this the title? If so, it should def. go in the "title" field.
Summary Info
Definitely the "description" field.
Keywords
I think these can either be placed in the description field, or in the subject field. If we actually have some home-grown subject headings, then we ought to put those there and put keywords in the description field.