The Chinese version of the SKS was not made until 1956. That is why it is called a Type 56. Serial numbers were NOT unique- when they began to import them, had to add additional numbers to make them legal.
That bolt is a cross bolt to reinforce the stock. You do NOT remove it to take down the rifle. Here are instructions- http://www.pistolcraft.com/sks/
Check carefully to see if your rifle has an import stamp (name or initials of importer, city, caliber) If NOT, do not fool around with it. Strong chance it was a war trophy, and not having that stamp runs value up quite a bit.