Miata Coolant Neck Blockoff
If you did a coolant reroute, and your new kit didn't come with a neck blockoff, look no further. This kit comes with both a block off plate, and a freeze plug to hammer in to the head. A slight bead of RTV between the head and the plate, and you'll be double certain that the port will never leak. The plate is thick enough to reuse the factory hardware.