Thought of something else you might try if you have the room. Make a retainer to cover the hole for the plug, drill a couple of small holes and put in a couple of small sheet metal screws to hold the retainer. Wouldn't take much. Yes there is a chance it could crack if to hot. If not mistaken that is cast steel. But if I'm not mistake I believe they weld up those holes and remachine when they Recon them.