I think it was a while after the CB750 was released in the states before it was actually sold in the japanese domestic market. I remember reading this somewhere, hence the lack of them in japan.
I imported my K0 (later in the run - 1042xxx) from japan a couple of years back. Its currently under restoration. I just wanted to ask Landing007, if yours has the speed warning light too. mine has the light, but not mechanism to activate it (wires cut) so I would love some pics if you could organise it. at least it gives me something to try and source as at the moment I have no idea of how it works!
Jap market machines differ in that they have KPH speedos, straight bar main footpegs (i.e. not spring loaded like the US models, but still round), the obvious speed warning light, and I think (from pics I have seen on Japanese models on ebay) an extra 'tang' on the side stand to make it easier to put it down. I think some of the later CB's had this as well. Aside from that, not much different however I have seen bikes with K1 numbers, but K0 bodywork, and carbs which are japanese domestic models too. Maybe for their own market they just used up the surplus stock? Hence Sandcast type frame with a later VIN.
Im afraid mine was a bit of a bitza and nowhere near completely stock - this info just comes with what I have seen from seemingly original K0 Jap market bikes.
vnz00