I took the speedo cluster out of my 92 parts bike today and installed it in my mates 89 as his lenses were cracked and his tacho was playing up. As my speedo showed 20,000km more than what his bike has I took the mechanism out and spun the extreme left reel 2 clicks back from an 8 to a 6 to match his km. Yes you could do this if you were up to no good, so no lectures please I'm well aware of what can be done if you're that way inclined. I'm just posting saying its an easy job if you need to do it for the right reasons. Pics attached. I was going to buy some of the gauge faces that are on Ebay atm but decided against it as once you take the needles off, which btw was an easy job you can't be sure that they are going back on in the correct position. I have a signwriting friend doing some decals up for me to place onto the existing gauge faces. I will post up once they are done.

 

To line the needled up, have a look from behind so you can see the mechanism. Move the needle and you will see the wheel move in the housing at the back. Hold the needle at a specific speed and mark where the wheel is in relation to the mechanism with a marker pen. When you assemble it will be spot on

 

You can also correct slight speedo errors by doing what David suggests.