it was registered IN THE uk on 19-03 80,making it a 'V' registration, engine number ;CB750E-2736355 FRAME NUMBER ;CB750K-2735369 ,color excel black, oil tank hidden behind side panel, 17" rear wheel,according to this info it's a 1977 but registered late in 1980 , but still a K7
http://www.sohc4.net/index.php?title=CB750K7