the speedo should stay correct as it measures axle rotation and not driveshaft rotation, the only snag would be if the input flange is different on the diff, don't get too many 530s so i can't remember what size flange they run but theres a couple choices on the e32 depending on production month, they can usually be swapped but if you overtighten it it can destroy the pinion bearing on the new diff in short order