Hi Richard,
That is a good question. You don't need a wear plate on the bottom. The back of the hook is slanted so it does not scrape the bottom of the stock.
Also the hook does not need to be deep. The deep Thompson Center style is silly and totally unnecessary. With a deeper hook, you may need to notch the back so it clears the rear lock bolt.
Make that notch very sloppy as shown in the photo so the barrel can be removed without the rear ock bolt needing to be removed. I urge you to consider two other details. First, make sure the standing breech has either a lug on the bottom for a cross pin through the stock or a threaded hole for a screw coming up from the trigger guard. That anchors the bottom of the breech securely so no levering by the barrel will raise it. Second, taper the slot in the standing breech so it narrows toward the top and do the same with the hook.
That assures a snug fit of the barrel when seated in the breech.
dave
