Overheating at idle

I DO NOT CARE what your timing is mine does not overheat running even just 5 degrees and parading.

With the car stopped, the hood down, and the engine idling
There is only one thing you need to know which is this;
Can your rad bring the temp down about 30 degrees between the fluid coming in and the fluid leaving?
If it cannot, and the rad is of a reasonable size, just figure out the why of this and fix it.

My guess is that there is not enough airflow across/thru the fins.
Your choices, in no particular order, are;
1) go to a direct drive shrouded fan, and retest. Make sure only fresh cold air is being pulled into the rad.
2) add fan blades
3) drive the fan at a faster rpm
4) drive the pump faster, and/or add vanes and efficiency
5) make all the hot water go to the rad, ie, restrict the bypass.
6) make sure the hot air can exit the underhood
7) supply fresh cold air to the carb.
8) when all else fails, consider if the engine is creating more heat, than would be normal. Ie is the idle timing really that late, or are the ring gaps too tight, etc.


FYI
My rad is and has always been, a 1973 A/C rad off a 318 car. It is installed into the original 19" core support. I run a 195HV stat, the HV pump, a 7 qt oilpan, the Airgap intake, and a a big hole in my hood sealed to the airhorn. I installed a Direct drive 7-blade fan, and it still ran hot.
In my case, the heat was coming from too tight ring gaps. After I opened them up from a gap factor of .065 to .085, the engine ran much cooler so I heated it up.
First thing I did was to install a THERMOSTAICALLY controlled clutch on a 7 blade fan, which now controls the temp to 207*F, cycling in and out as may be required.
I haven't more than glanced at the factory temp gauge since about 2001. I run whatever timing I want at idle, from 5* to 20*, adjusting it from the front seat with my dash-mounted, dial-back, timing module that has a range of 15 degrees.
As far as I can tell retarded timing at idle that causes atomic meltdowns is greatly exaggerated. Get your Transfer port set right, and the Idle-AFR close, and in my case, the engine could care less about IDLE-timing.

Oh, I forgot, my engine is a hot lil 367. It has had three cams in it from 270 to 292 intake duration; and Cylinder pressure from about 180 to as much as 195 psi, and as for cooling and idle-timing, ran about the same with any of the cams, once the rings were loosened up..
It has gone 93 in the Eighth.