I searched "executive japan" in google (search string: executive japan site:bikeforums.net) and came up with this thread, suggesting a Centurion Executive exists:

http://www.bikeforums.net/showthread.php?t=43176

Then I searched the Centurion database thread, post 62, and it appears your S/N is close to the format, but not exact: http://www.bikeforums.net/showpost.p...9&postcount=62

You might also try searching the Nishiki S/N database...and maybe there's another for a Japanese brand? I can't remember.