Pull back the plasic knob on the back then the "rota breach" rotates out to the side behind the feed neck, number should be under there. Im sure you have done it anyway as you described the face of the bolt.
And yes your right they are cracking gats I hope it goes to a good home.
nevermind im in newcastle and the ypc xmas bash will be the furthest south i'll be traveling anytime soon but i should be able to aford postage no probs