Original film archived blueprints with pedigree (i.e. original Northrop proprietary) are likely worth a princely sum to the right collector. Therein is the key. You need to research where these collectors might gather. Just putting them on Ebay may short shrift you.
Do you have any indication that the film archiving of the original blueprints are Northrop property?
Do they have original Northrop drawing numbers on them?
Is there an introductory configuration management document that tracks contents, changes and resultant version numbers?
Are these films complete (not likely for the whole airplane, they must be airframe, hydraulics, electrics, avionics, powerplant, fuel management, or portions thereof, etc)?
These are the types of things that collectors will assess to determine overall value.
Best of luck!