First thing I'd do is strip it, wash it with TSP (a commercial cleaning chemical, dirt cheap, available at any Canadian Tire and it works amazingly well) or clean it with oven cleaner and a plastic kitchen scrubber with kitchen gloves. Lots of compounds work for the cleaning, including brake cleaner, but don't get this one on your hands.
After you've stripped it, see if there's any dents you want to remove, this can be done by using a hot clothing iron and a wet cloth over the affected area, it will raise dents.
After this, start sanding, the grits I'd recommend are 320 for most of the work as this is already a finished stock (buy quite a few sheets, like 3 to 5, they're cheap), and then I personally would like to move up to 600 grit after the 320, it will be time consuming but give
amazing results in the final finish. So buy a few sheets of 600 as well if you really want this to shine.
After that, for the finish, I'll recommend the easiest finish for you to apply in my opinion and the end result is first rate. Buy "Tung Oil" from Canadian Tire or your local hardware/home reno store, and once the stock's sanding is complete, you apply this with a simple rags in coats. For the first few coats, just rub it on liberally every 24 hours (I cut the gap down to 12 frequently with no adverse effects). After the first few coats, you'll see a lustrous finish building, and now you start using less tung oil and rubbing more with the rag. Rubbing the tung oil moistened rag on the finish is capable of producing almost a glass-like finish, just a matter of effort and time. It's a rewarding experience and less work than you'd think.
I did the stock below in exactly the fashion I've talked about above, and it all started with an ugly old USGI stock that I guarantee looked worse than what you've got there to start with.
