Agreed, I was writing the same thing at the same time. Make a new plate.
I have found that to make a patch match the old it need to be from the same piece of wood and cut with the same grain orientation. And then making the glue line disappear is hard, I usually use a milling machine to get dead flat surfaces.
I have a wonkie precarve to tackle soon. I know the trigger plat inlet is wrong and oversized. The trigger plate is brass, simple, and a poorly done casting. I think I will make a new one and ash can the one supplied with the kit. I hate patches and inletting gaps.