I have cleaned many old military stocks with Easy Off Oven Cleaner, or just any generic spray on oven cleaner, a toothbrush, and water.
This will remove all grease from the surface, and will remove whatever "surface" finish the thing had. Most military rifle stocks were dipped in a bath of linseed oil with coloring. Your surface finish is a combination of dirt, grease, old oil, and maybe some original linseed with coloring.
The Japanese used a lacquer, this is not common.
I recommend wearing dishwashing gloves, and goggles. And doing this outside next to the garden hose.
Take all the removeable metal you can off the stock. Don't spray oven cleaner on the remaining metal if you can.
I spray oven cleaner on the stock, let it sit for a couple minutes, and then rub the surface grease off with the toothbrush. Hose off cleaner, and repeat as necessary.
Do not let the oven spray dry on the wood or you will get a funny surface appearance. Do not dry the stock in a hot car!. I did that, and it cracked a stock. I dry the stock with a blow dryer.
To remove dings, set a standard iron to "steam". Put a wet cloth over the ding and steam the thing out. If the grain is not cut, you can steam out some big dents. If the grain is cut, there will always be the cut mark.
After the stock has dried, to remove the wiskers, go over the surface with 00 or 000 steel wool.
I will coat the surface with boiled or raw linseed oil. This takes forever to dry, but is consistant with what the US did. You can also purchase red colored stock finishes that duplicate the reddish color found on US stocks, or you can just let the linseed oil dry and have that European look. Tung oil should be an excellent wood perservative, I just have never used it.