So far, good job on the "patch". If that's a Bucks County, either the buttstock is too small or the Pbox is too big....just an idle thought.
W/ a vertical wall to mount the hinge plate, a red hot. length of round steel is burned in...this may take a few "burns" to get deep enough. Have done this on all my BC LRs. The round steel is undesized of what would be the "tap drill" dia. because of the overburn.
Is that a ledge on the hinge side? The vertical wall for mounting the hinge plate goes straight down....no ledge. Perhaps it's the photo?
Again....good luck on your build.....Fred