Not only would you need the new instrument pod but you would also need a dealer to "code" it to your car.
I while back I posted some speedo decalls I saw on ebay.de (the German website)... I think those look better than the M1 ones. Have a look here:
And... ofcourse you could also just get a M3 instrument cluster and have that coded to work in your car. That looks the best IMO.