Fr. Mariusz Zajac,
That fish is not only BIG, it is also in very good shape. Usually, a fish that large/old has some scars, fin rips and tail splits. That one looks like it's in prime shape.
You oughtta have your taxidermist make a replica (blank) out of it - or at least a half cast before he cuts it to be mounted. Or if he doesn't do that type of stuff I can hook you up with somebody up your way that makes some of the best blanks in the world: Ron Reynolds in Bath Ontario runs Realfish Reproductions. WWW.Realfish.net
is his website. He and his son Dave are some really nice guys and you won't be disappointed in their work...