451 overheating, even when moving

That's a nice setup. Understand when I say this, I take NOTHING away from it whatsoever. However, you have one HECK of a radiator if it never has idle temps above 190........and I believe you. "Most" high performance engines do require that magical "around" 4000 CFM number in order to keep cool at idle or slow speeds. That's a nice install you did blocking the overlap areas as you say. Most people don't think of that. Do you have pictures installed? I'd love to see it. I'm sure it's a neat fit.
Happy to share! I always say "Your results may vary" but for me personally, I look at everything anyone else does and posts to learn and see what may have worked for them.

In that spirit, here's a couple shots when I did the install. Note that I assembled the fan assembly to the rad before installing it in the car. There were no open holes or airflow bypasses when it went into the car. Wiring was not yet done here in these pics. Note that I have an overflow bottle hooked up that was not shown in the pics. Also, the hub of the water pump has plenty of clearance as it falls in between the 2 fans motors. Lastly, due to a glass 6-pack hood, I do not have a rad support to hood seal.
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The final overall package:
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