you can get a 2 module rcbo that fit those boards seen them on a couple of boards ive tested though i dont think you can buy them anymore.
Yeah, they're ABB ones. I have though on 1 occasion fitted Wylex NSB RCBOs to the last 3 ways in one of them old boards. They were the only ways that didn't obstruct the neutral bar. It was a tight fit but everything went back together as it should of.