The large (huge actually) mains of the 351W are what make the bottom end so strong, but you are saying the smaller ones on the 351C make it more durable. What gives?
The only cooling problems I've seen with Clevelands stemmed from yay-hoos, installing the head gaskets backwards. This creates a dramatic "explosion" thru the radiator once the trapped coolant flashes to steam when the engine heats it enough. This catastrophy doesn't happen with the Windsors, due to the coolant path. In a Cleveland, when the head gasket's installed backwards, the coolant flow is stopped where it returns back to the block from the heads, in a Windsor, the coolant just shortcuts the heads.
There's also the little metal plate or disc (brass restrictor ring) under the thermostat. People don't know about it and leaving it out or accidentally using a Windsor thermostat can cause problems.