Hey there. Way to go finding an old discussion that’s pertinent to your issue. Good searching. And fun to see an old discussion like that and what we were going through at the time.
But just so we’re clear here, 210 is not bad. It’s not only not overheating, but it is in fact where modern engines tend to run from the factory.
Even though many of our engines had 180° thermostats, it wasn’t long after our trucks were built that they went to 195’s instead. Which is what a lot of us use in our Broncos today.
So you’re not in any kind of a danger zone if you were concerned.
The fact that it cools down when you rev it up is actually a good sign. That means most things are working and your .040” over 351 is not experiencing hotspot issues.
Or at least not bad ones.
Over-boring Windsor engines has been problematic for decades.
Sounds like yours is not one of the problem engines with core shift issues.
Do you know what thermostat you are running? Is it a 180 or a 195?
When you rev the engine and the temperature comes back down, does it go to the rated temperature and stay there as long as you’re driving around?
Maybe a little aux electric pusher fan would be a great thing for the stoplights, but with the limited space that our rigs offer, there are not many options.
Sounds like your set up is pretty nice, but may be a little testing is in order.
If you’re driving around sometime and pull up to your house and idle it, see if the temperature comes up. If it does, pop the hood open and see if it comes down on its own without having to increase the RPM.
If it does then perhaps one of those other options such as the fender skirts, radiator ducting, hood louvers or electric fan would do the job.
If it doesn’t come down on its own, or frankly just to check anyway, you might just verify your ignition timing while you’re at it.
Advance it as far as you can and still have it run right.
That usually helps engine cooling even at idle.
Good luck!