This little gems are from a small group in the files of the then Harman Kardon Industrial Designers. They are of course highly detailed and very likely one of a kind. Check out other auctions for similar packages revolving around other units.
You get a total of 3 blueprints in their original Shin-Shirasuna Electric Corp. folders (2 folders). At a later point Shin-Shirasuna apparently bought much of Harman Kardon's audio division in 1979 and had already been providing the design work for the company.
Also included is an internal Harman Kardon HK 2000 photograph and dealer preliminary product announcement.