Farmdude,
Instead of just cutting the stock down on the 243 you already have, why don't you look into finding a replacement stock that yo can alter, or a replacement stock to take the place of the full length one you have. That way when you're done you won't have turned the rifle into a one person gun or a one size gyn. With the other stock you'll be set for when the young'n grows, or when your daughter-in-law wants it back.