Need these (2? Or maybe it’s one piece) what is it called?

so my friends mustang gt (2000 convertible) is leaking coolant and thinking it was the heater hose that runs under the intake, I instinctively changed out that first, which granted did need changing anyways, but coolant still flows right out the back side and this part is missing from his rear passenger side of the valve cover to the block, I figured something went in that little slice because of a clear impression of fresh metal being there but I can’t find out what part that is, it’s like a support bracket of some sorts? Idk but it’s missing and leaks the coolant straight out the back from that crevice, anyone know what it is called? Where to get one? I’ve looked everywhere