thats bad luck

what do you want to do with the rifle now? I suspect this rechambering was done in scandinavia once and now you have a rifle without proof? in any case the extractor have to be adapt for the 10,75x68 rim and the rifle need a new proof( what will be happen without problems I suspect)to hold it or sell it.
remeber this when I see a rifle for sale what will happen sooner or later