another 360/408 over heating

I don't have the exact answer for you. But I do know two things. 1 You can stop buying and replacing thermostats. They are proving they are working. When they say 195* that means they fully open at that tempature. Not that they will keep your motor at that temp. In each case they prove they are opening and doing their job. 2. I would not have cut those holes. You want everything sealed up on the fan side. You only want it pulling air from the side of the radiator. Any pull from the fan side is wasted. #3 for ***** and giggles. I would not use the napa high flow pump. You can pull the fluid so fast that heat doesn't transfer. You are kind of showing that with the lower temps in the radiator. Lastly, the most thermally efficient at conducting heat and moving it is water, snake oil be damned. I know I know I hear the arguments.

Run a pressure test on the radiator system.