As Jack has suggested, do try releiving that tension of the forearm and I think you'll see immediate improvement.
Something to watch for with these guns, especially the older ones, is that over the years, many folks while cleaning their rifles, or oiling them, will get quantities of gun oil on the stock and forearm. The wood will absorb this oil over the years, and the wood will swell, making it nearly impossible to remove the forend of the 336's, especially those with the 3/4 length magazine tubes (holds true for .444's, .45-70's, .375 Wichesters, and .35 Remingtons), as there is the forend hanger dovetailed into the barrel, and no place for the wood to go as it swells. This can cause some serious pressures on the barrel as the wood swells from oil soaking over the years. The only cure is to pull the fore-end and go to work on it. Often times you'll see remarkable improvements in accuracy once done.
I don't know if this applies to the gun you are working with, but thought it was worth mentioning!
God Bless,
Marshall