Unless you SKS is loose I'm not sure if this is needed as most SKS's I have seen are very tight in their stocks already.
No long ago someone here had posted pics of a bedded in SKS to one of those plastic stocks...they used some sort of metal epoxy, try a search and see if you can find it. This is for bedding only of course, as you still need to be able to take the rifle out of the stock for cleaning.
Hope this helps.