Cooling System Circulation Question

I am going to try installing a circulating coolant heater into my VX. Help with cold starts. It's 25 degrees every morning when I leave and I've heard of guys who can get the engine up to full temp with their heaters...
Anyway, there is a tutorial on this page -Here
This guy makes it sound like you have to have the input coming from the block plug, but the instructions say that the radiator drain plug is an acceptable alternative. I've seen another guy just use the lower radiator hose. If I will be taking fluid from the radiator, and them pumping it into the heater core inlet line, it would then circulate back to the block. Would that not work?
Anyway, there is a tutorial on this page -Here
This guy makes it sound like you have to have the input coming from the block plug, but the instructions say that the radiator drain plug is an acceptable alternative. I've seen another guy just use the lower radiator hose. If I will be taking fluid from the radiator, and them pumping it into the heater core inlet line, it would then circulate back to the block. Would that not work?