There are other options.
If you are only running hot at idle, then the rad has enough capacity;you just need to increase the airflow thru it.
You have to make sure that the rad is unobstructed, that the fins are unobstructed, that they are not all bent up, mangled and full of dirt. If this is an A/C car, the above goes for the condenser too.
Then once it is proven that the air is able to come thru the rad, you have to make sure it can get out from behind the rad.
You then have to look at the fan system, that it is actually moving air, and that the air that it is moving is coming through the rad and not just recirculating around the tips of the blades. So that means you need a shroud and that the fan fits tight into it. In other words if the shroud has a 19 inch opening,you need to put at least an 18 inch fan into it , and get it centered as best as possible. Then the fan needs to also be centered into it in a fore and aft direction. I would run it with a direct drive to see if the system now works. The fan should have a certain number of blades. I like 7. It's a very good number. I like the Mopar all metal 7 blader. I have run less on low-performance cars, but as the power goes up they like to idle hotter. I had zero success with the one 6-blade flex-fan I tried.
After this if it still runs warm, on my SBM I installed a hi-flo pump, which is nothing more than an 8 blade pump with an anti-cavitation plate mounted to the vanes. IDK if you can one for a BB.
I run a minimum water temperature of 205; without problems of any kind. Because I have no problems, I installed a thermostatic clutch fan from an early 2000 Ford pickup. And still no problems.
At idle The rad has to pass air, and the fan system has to work!
