differential

I have a 84 318i and the differential is goin to need to be replaced in the near future. I have heard that a swap from an e30 325 is possible and will give my car a little more power. I also will want to swap out the old drum brakes for the disc brakes that i would aquire from the 325. I was wondering how easy the diff. swap would be and if it would be worth it. open to any suggestions or comments.

Thanks