I agree that you shouldn't try to add the patch box. That stock has some very pretty figure that might be hidden by the box.Never heard of the CVA Mountain Rifle without a patch box. The CVA Big Bore in .54 and .58 yes but not an actual standard Mountain Rifle. I wouldn't add the patch box if it were me. I would leave it as it came. Could be one of a kind in fact. I would also double check the bore diameter over what the barrel stampings are if it were me.