M & P sell the speedo convertors too.
As mentioned earlier, you do need the blue Honda one. Mounts up on the clock itself. The gold one is differently geared and mounts down at the bottom of the cable, so no good for the NSR. If you do fit this one it makes the speedo over-read.
I fitted one. Took the cover off the speedo and stuck the supplied Mph decal over the Kph sign on the speedo face. Gives an opportunity to give the inside a good clean too.
I`ve seen a picture of the early Blade clocks in a magazine. They do look exactly the same as the MC21 clocks to me.