If the electrical harness is original, and other signs suggest things have been not switched over, I'd suspect perhaps a top end overhaul which included a new head and maybe the cylinder block serviced as well. The engine looks hand painted as well. Looking at the paint and other bike's components closely might show what had been done and uncover it's story.
1982 Kawasaki KZ1300 A4
Building an engine from random parts. This will eventually morph into building a bike from random parts - if it ever happens. Need a frame to begin with.