I ran a lot of pre 80 Mopar motors on dirt tracks. Without a doubt, I can tell you 210 is not a problem, unless the cooling system is not pressurized. Water in an open pot doesn't even boil at 210. With the cooling system under pressure, 225-235 is hot, and those old Mopar motors did OK unless it stayed at that 225-235 for 10 minutes or longer, under pressure.

Next up, factory gauges were a best guess as far as actual temperature is concerned, the "readings" were generally all over the board, I doubt many were even close. Just because you had one that was in the hot range at 210, I've had several that probably were just into in the operating zone at 200. If you are basing your overheating on a factory gauge with an assumed overheating temp of 210 because of one factory gauge, you probably don't even have a problem you think you have.

3rd, if reving your motor did not effect the temp, you either didn't reve it steadily, or properly. You should have brought the rpm up about 500 rpm, and held it there a minute or so to see if the temp started dropping. If it would have failed to drop then, your perusing air or water flow probably isn't your issue anyway, because that extra 500 rpm would do the same thing as more air or water flow.