Chasing this cooling issue for months

I don't see anything wrong with 175. That's just a product of that badass radiator. What I see is, that it should be running 175 pretty much in any situation and here's my reasoning. If it runs 175 on the open road and heats up at idle, that's an indication that there's not the same airflow at idle. Besides that, I can tell you just from the footnote on the Summit site that 2400 CFM ain't enough. As a general rule of thumb, most V8 engines need around 3500-4500 CFM to stay cool at idle. So if it were mine, I would do one of two things. Either leave it alone or get a higher capacity fan. Remember that it's not just the maximum temp that the engine acheives. It is also how long it stays there.