First- reality check- Numrich sold out of stocks and magazines for those a long time ago. When they had them, a stock and mag would cost you more than the gun is worth. Really. The price was $130, plus shipping, and a bolt action 12 g is worth about $70-$75.
Second- want to do some cleanup? Nothing wrong with that.
Remove action from the wood. Formby's Furniture refinisher makes a good start for many. Be careful- stuff is flammable as hell. Do not sand unless wood has splinters.
For the metal parts- go to the grocery, get a COPPER Choreboy pot scrubber. Not copper plated, but copper. Wet the metal good with a light oil, let set for a couple of hours. Wet the choreboy with some more oil, reb lightly. Gun will turn coppery color. When you are finished, use soft cloth with a couple of drop of oil, polish gun. Copper color comes off.
I am not a gun snob- I have several bolt action shotguns, but understand they do not have high values.