I've got one! It's a slightly later model than yours, but the mechanicals etc are pretty much the same. You can't have it.
There's much conjecture about being a bsa copy. It did have that obvious style of the day and K'saki did acquire certain rights from bsa in the early '60s but, Well, I'd go so far as suggesting bsa never built anything for shopfront sale (with this sort of engine/drivetrain) as well engineered as did K’saki for the old W models.
The old W's were born at the wrong time. Too late. Bagged in some reviews and grudgingly praised in others it seemed. Poor market acceptability etc etc and.......that was a shame, because they really were a good bike..Overnight the mighty 4's from Japan swept all before them and the K’saki W only survived as long as it did, as a four stroke alternative , until the launch of their 900. The rest is history, (as they say).
The twin carby version was claimed to be good for about 115mph/>8000rpm. Not bad for a stock parallel 360deg twin,OHV 624cc. Well, I don't personally know anyone that did it, but I do know it likes to rev and will (arguably) do it more reliably than any of the similar configuration brit bikes of the day . And, they do it without leaking. Another plus!
.....and, relatively straight forward to work on and maintain, for its ilk.
Yes, most of the parts are difficult or impossible to come by. I cant find any direct Kawasaki supply of anything meaningful anywhere. For example, the crank is one piece. Meaning, you can't separate the rods and bearings (and re-assemble)in the backyard shed. It's pressed together. Clutch parts might need to be made. The head is like gold and replacing valve seats successfully might be an issue. Most gaskets can be cut by hand, except the head gasket. Can be made. Certain other frame parts are interchangeable with other models of the time. Probably still are examples out there in one condition or other, waiting to be brought back to life, just a matter of finding them. I know of a few, but can't get'em (yet).
...... I'm lucky so far because most of mine remained in very good order, even after 25 years of non use/abuse.
If you like the sound of a 360deg parallel twin, you’ll luv this one. I’ve even seen one with 2:1 exhaust. Sound is awesome.
I’ve tried to attach a few pics of mine taken during a recent rebuild. It’s running now, but still needs some work on ‘cosmetic originality’.
Lets see what you’ve got.
If you need other info let me know…………...