One of the experts would need to chime in here to tell me I am blowing smoke because my only experience is with the 580 and 720 engines.
Looking at the service manuals, and specifically the cooling system, of the various engines the cooling flow is different. Some have a "T" in the cooling circuit from the pump to the works; one output from the "T" goes to the exhaust system and one output from the "T" goes to the engine. Ya gotta look for your specific engine. From my small experience the engine/cooling jacket is a closed system with no connection to the internal workings of the engine. It appears that the risk for getting water into the innards of the engine by towing is from the cooling to the exhaust back into the exhaust ports of the engine.
If all my blather above is correct, the best place for the clamp is between the pump and the "T", if it exists.
Yes, Lou is correct regarding the risk, but to distill the word hydrolocking down into simple terms that even I understand, it means filling up your engine with water.
Rod