Overheating 360 new engine

Drilling the stat makes it worse because it reduces the pressure in the system. The pressure reduces localised nucleate boiling [ air/steam bubbles ]. The reason that drilled stats appeared on the scene is that Stewart Components, maker of race water pumps, eliminated the bypass in some of their pumps. To ensure there was pressure relief in case of a stuck stat so that the engine would not blow out a Welsh plug, the stats were drilled. Your engine has the bypass, as do all production engines.