The other folks who responded here are correct. You can receive the property and consider it for acquisition just like any other proposed contribution to the collection. I'd advocate for accepting the bequest if it is unrestricted, accept what you want, decline the rest, and dispose of the declined materials to a sale. Because these items were not accessioned, any proceeds derived from sale are not restricted to care/acquisition.
I like CMP's to state that "bequests to the collection are considered for acquisition at the time they are legally and physically available for transfer." This helps you have good conversations with people who want to give you a load of materials that you may or may not be able to steward, and which may or may not fit your mission and scope of collection, when the person actually dies.