Funny that this brand should come up just now, a Yasuki Strat neck just sold on Ebay:
http://cgi.ebay.co.uk/Yasuki-1970s-Japa ... 0296329553
I've never heard the name connected to Matsumoku - but that doesn't mean it isn't. However there were a lot of different Japanese manufacturers, all of whom seemed capable of producing high-quality instruments.
If you can post some clear, detailed pics it might be possible to identify the manufacturer - details like hardware, neckplate, electronics, neck construction etc, and anything stamped, written or marked anywhere on the instrument can all provide clues.
Is the humbucker original? If it's a 70s guitar, I'd think an HSS configuration would be pretty unusual.
Jon.