you DON'T have to use 2.5RS axles for the diff swap. The inner stubs are the SAME. This applies to all the newer R160 rear diffs like from '97+. The ABS trigger in the rear has ALWAYS been on the hub. It changed in the front... from HUB to axle trigger.
I've put a VLSD into my '99. I've put it on a '98 RS.....NO issues.