SC, I can only guess that you don't like the big gap that will develop alone the sides of the barrel channel.
Why not just take a thin strip of wood/plastic/alum and fill in closer to the barrel? Glue it flush to the top of the stock foreend (1/4" wide should be plenty). Leave the forend hollowed out to keep the rifle balance (you might need to hollow it out more to get the right balance). Once sealed and painted, who can tell?
Then if you want to return to a larger barrel, you don't need to hog out the forend again.
Jerry