Speedo drive !!!!!

[breakdown]

Right, I've got an A2 which I'm in the process of sorting out, it is fitted with the later model alloy wheels, I had assumed that the speedo drives where pretty much all the same. I have just purchased a speedo cable for an A2, but when I went to fit it I found that the drive has a smaller dia screw (speedo cable bushing).
According to the parts book that I have, the Z1R is fitted with the same style alloys and has a diffrent part No for the speedo cable.
So am I right in thinking that I either get a speedo drive form an A2 (and hope it fits the alloys) or get a speedo cable for a Z1R or later model.
One more thing I no nothing of the history of this bike so it maybe the wrong speedo drive altogether, it seems to fit the wheel ok and works when the wheel turns!!!!!!!!!