your first post sent me searching the www for info on the W1 and W650.
although it looks like a blatant rip-off back in the 60's with the W1 series, when Kawa tried to tap the Retro demand in Japan with the W650 I give them credit.
(blatant rip-offs aren't that uncommon anyways - re: BMW / Ural / China-brand-whatever-its-called)
wasn't it said that "Imitation is the most sincere form of flattery"? I find the drive shaft to overhead cam quite elegant.
I'd like to ride one - and if the seat height works for my girl, get her on one too.
This is a good website with links.
Ian Chadwick seems to have a pretty deep knowledge base of the Brit bikes as well.
good luck on yer quest.