Speedo/odometer problem!!!

My speedo packed up recently on my 98R 2.0 GLS galant estate, and was told by the dealer i would need a whole new instrument cluster. As money was tight i managed to get one from a breaker yard with 100,000 plus miles on the clock (mine was approx 80,000 when the speedo packed up, odometer was working fine!). As the mileage was greater than the original, i decided to "adjust" the mileage to match the original. Unfortunately, when we fitted the cluster, the speedo now worked, but the odometer won't budge! What i want to know is, is there any way i can remove the speedo from the latest cluster and insert it into the original??? Also, how easy is it to do and where do i start! (a friend at a garage swapped them originally but he's moved away!) PLEASE HELP!!! :cry: