If the barrels have separated by that much, I suspect something else has occurred, possibly a bent barrel.

I believe that Marocchi in Italy took over production of the 512S Finn-Classic series. Likewise I was once told that barrels sets for the Marocchi rifles could be fitted to the Tikka actions (Still required proper fitting). Might be worth seeing if they have an agent in your country who can advise. A new barrel set may be a better alternative than a repair to a potentially suspect barrel set.