And from memory the smaller capacity South African (only) NS400 had smaller diameter pistons, didn't it (56 instead of 57mm)? IF these are the right size - it may open another avenue of enquiry. This was what was specified in the ebay listing, which appears to have ended. The seller still has a heap of bits listed, and you could probably contact him to see if they sold, or he has another set.

I am not in any way connected with the seller - I just happened to notice the items prior to reading this thread. And on the chance that they might be suitable and get someone out of trouble - refer to Andy's post #3.

Cheers

Scott