Was just comming in here to say, that if you can find the newlec range of about 5-8 years ago then they appear to be identical to the havells prosafe stuff (you have to look closely at labels to see there is braker with a different name in the board. It does say 6ka on it, and while I suspect its effectivly been downrated to suit requirements, I'd only fit it where the PFC is actually less than 6kA. But providing thats the case, then I would not have any issues fitting the newlec stuff in a havells board as its not really mix and match in my view, its badge engineering. Like MEMshield 2 and Bill tailsman plus. Crabtree and siemens (and now I think the new version of the newlec stuff).
Strange that the newlec stuff was based off prosafe rather than homesafe, but it was, I've got a C63 prosafe MCB fitted in a havells board here that I ordered from newlec just before the range changed after I found I couldn't get a havells one.
I'll have a look think I might actually one of what you want (and actually havells) in a box in the garage ceiling, will have a look later/tommorow