[Jack21]

Have a very similar setup. 351W, TFS aluminum heads, Edelbrock hi vol water pump, 180 deg thermostat, Griffin rad, Scotts 16" fan. Used stainless 1 3/4" exhaust tubing for lower water crossover with 3, 90deg elbows. Using a 7 pound Stant cap. Temp runs 180 while cruising, gets up to 205 when fan kicks in.
Also using coolant overflow bottle because engine "breathes".

My first thoughts would be head gasket or cracked head. Any white smoke coming out either exhaust?

We're getting gas (steam or air) into the cooling system, which gets into the water pump, pump looses prime, and no water flow. Or blockage in the radiator if bottom of radiator is cold when engine is running.

Mine was a mutha getting all the air out of it when first fired up.

A test. With garden hose keeping system full, take the upper hose that comes out of the thermostat fitting. Hold it up in the air. With engine running, idling, what should be coming out is water. No water? Pump isn't pumping. Water and bubbles? Gas is entering cooling system.

Next test. Set the plug wires up so you can remove them one at a time with a plug wire removal tool. Insulated. Hook up a tune up tach. Remove plug wires one at a time. RPM will drop. This should be a constant drop except the leaking cylinder. It will drop less. And, the bubbles should stop, or decrease.

Let us know how this works out.