They're made in the same factory under the exact same processes, the timings of these engines are virtually identical, Novarossi piston & sleeves won't fit RB engines without a little modification. But they're essentially the same, so keeping an RB engine running beyond it's production life cycle is entirely possible using Novarossi parts, a Novarossi rod can be modified to fit an RB too if for any reason you struggle to get an RB rod.