you can very easily migrate your old odometer unit into the new cluster. it's in a rectangular plasic case held by 4 plastic screws on the backside of the speedo.
you have to pull the speedo needle in order to take the unit apart - do this gently using a fork or something like that as a lever. also, be gentle when pushing the needle back, don't push it deeper than it was.
will take you less than 10 minutes once you have the two clusters on the table in front of you.
Tiv