Wavetrac makes an aftermarket rear diff for the 335d. I *think* most 335d diffs are welded, though saw mention of very early 335d's being bolted (03/2007 and before).
Given that, you'd probably need to have your ring and pinion machined, plus the usual new hardware (gaskets, driveshaft/axle seals, etc.). You'd need to find a competent shop to take care of the ring and pinion, as well as make sure your bearing clearances are properly shimmed on the new diff. Then it's just a matter of coding off your ediff with protools or ncs. Don't know why you'd need to use different axles or driveshafts if they fit your OEM diff. Hope that helps, good luck!