Been there, done that. Never could get the fuel gauge to work (needs developer mode in Star-DAS) and the mileage will never be exact. The mileage displayed will be that of the cluster, not your car. If the discrepancy is too big, the ECU won't like it and you'll get 0's across the odo.

To even get them to plug in, the VIN will have to be flashed to seventeen zeros (00000000000000000) and then you will start the long process of tearing the dash apart.

External bezels will need to be swapped from the OE gauge to the SLK32 gauge, which is the easiest part of the whole swap.

Last but not least, your cluster will light up amber. There is no way to correct this, as the plastic screen itself is amber... the lights shining through are clear.

Photos in my gallery under my white car... This mod was performed on my Limited. I will say, they looked superb aside from the fuel gauge not working.